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With the
exception of the special type Item types representing element and attribute nodes may specify the
required ·type annotations· of those nodes, in the form of a ·schema type·. Thus
the item type Here are some examples of ·sequence types· that might be used in XQuery expressions:
2.5.4 SequenceType Matching[Definition:] During evaluation of an expression, it is sometimes necessary to determine whether a value with a known ·dynamic type· "matches" an expected ·sequence type·. This process is known as SequenceType matching. For example, an QNames appearing in a ·sequence type· have their prefixes expanded to namespace URIs by means of the ·statically known namespaces· and (where applicable) the ·default element/type namespace·. As usual, two ·expanded QNames· are equal if their local parts are the same and their namespace URI's are the same. An unprefixed attribute QName is in no namespace. The rules for ·SequenceType matching· compare the ·dynamic type· of a value with an expected ·sequence type·. These rules are a subset of the formal rules that match a value with an expected type defined in [XQuery 1.0 and XPath 2.0 Formal Semantics], because the Formal Semantics must be able to match values against types that are not expressible using the SequenceType syntax. Some of the rules for ·SequenceType matching· require determining whether a given schema type is the same as or derived from an expected schema type. The given schema type may be "known" (defined in the ·in-scope schema definitions·), or "unknown" (not defined in the ·in-scope schema definitions·). An unknown schema type might be encountered, for example, if a source document has been validated using a schema that was not imported into the ·static context·. In this case, an implementation is allowed (but is not required) to provide an ·implementation-dependent· mechanism for determining whether the unknown schema type is derived from the expected schema type. For example, an implementation might maintain a data dictionary containing information about type hierarchies. [Definition:] The use of a value whose ·dynamic type· is derived from an expected type is known as subtype substitution. Subtype substitution does not change the actual type of a value. For example, if an The definition of ·SequenceType
matching· relies on a pseudo-function named
Note: The derives-from pseudo-function cannot be
written as a real XQuery function, because types are not valid
function parameters. The rules for ·SequenceType matching· are given below, with examples (the examples are for purposes of illustration, and do not cover all possible cases). 2.5.4.1 Matching a SequenceType and a Value
An OccurrenceIndicator specifies the number of items in a sequence, as follows:
As a consequence of these rules, any ·sequence type· whose
OccurrenceIndicator is 2.5.4.2 Matching an ItemType and an Item
2.5.4.3 Element TestAn ElementTest is used to match an element node by its name and/or ·type annotation·. An ElementTest may take any of the following forms. In these forms, ElementName need not be present in the ·in-scope element declarations·, but TypeName must be present in the ·in-scope schema types·. Note that ·substitution groups· do not affect the semantics of ElementTest.
2.5.4.4 Schema Element TestA SchemaElementTest matches an element node against a corresponding element declaration found in the ·in-scope element declarations·. It takes the following form:
If the ElementName specified in the SchemaElementTest is not found in the ·in-scope element declarations·, a ·static error· is raised [err:XPST0008]. . A SchemaElementTest matches a candidate element node if all three of the following conditions are satisfied:
Example: The SchemaElementTest 2.5.4.5 Attribute TestAn AttributeTest is used to match an attribute node by its name and/or ·type annotation·. An AttributeTest any take any of the following forms. In these forms, AttributeName need not be present in the ·in-scope attribute declarations·, but TypeName must be present in the ·in-scope schema types·.
2.5.4.6 Schema Attribute TestA SchemaAttributeTest matches an attribute node against a corresponding attribute declaration found in the ·in-scope attribute declarations·. It takes the following form:
If the AttributeName specified in the SchemaAttributeTest is not found in the ·in-scope attribute declarations·, a ·static error· is raised [err:XPST0008]. . A SchemaAttributeTest matches a candidate attribute node if both of the following conditions are satisfied:
Example: The SchemaAttributeTest
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Comments may be used to provide informative annotation for a query, either in the ·Prolog· or in the ·Query Body·. Comments are lexical constructs only, and do not affect query processing.
Comments are strings, delimited by the symbols (: and :). Comments may be nested.
A comment may be used anywhere ·ignorable whitespace· is allowed (see A.2.4.1 Default Whitespace Handling).
The following is an example of a comment:
(: Houston, we have a problem :)
This section discusses each of the basic kinds of expression. Each kind of expression has a name such as PathExpr, which is introduced on the left side of the grammar production that defines the expression. Since XQuery is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.
The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For the complete grammar, see Appendix [A XQuery Grammar].
[Definition:] A query consists of one or more ·modules·. If a query is executable, one of its modules has a ·Query Body· containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol Expr.
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The XQuery operator that has lowest precedence is the ·comma operator·, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of multiple ExprSingle operands, separated by commas. The name ExprSingle denotes an expression that does not contain a top-level ·comma operator· (despite its name, an ExprSingle may evaluate to a sequence containing more than one item.)
The symbol ExprSingle is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be an ExprSingle, because commas are used to separate the arguments of a function call.
After the comma, the expressions that have next lowest precedence are FLWORExpr,QuantifiedExpr, TypeswitchExpr, IfExpr, and OrExpr. Each of these expressions is described in a separate section of this document.
3.1 Primary Expressions[Definition:] Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.Constructors are described in 3.7 Constructors.
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[Definition:] A literal is a direct syntactic representation of an atomic value. XQuery supports two kinds of literals: numeric literals and string literals.
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The value of a numeric literal containing no "." and no e or E character is an atomic value of type xs:integer. The value of a numeric literal containing "." but no e or E character is an atomic value of type xs:decimal. The value of a numeric literal containing an e or E character is an atomic value of type xs:double. The value of the numeric literal is determined by casting it to the
appropriate type according to the rules for casting from xdt:untypedAtomic
to a numeric type as specified in .
The value of a string literal is an atomic value whose type is xs:string and whose value is the string denoted by the characters between the
delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.
A string literal may contain a predefined entity reference. [Definition:] A predefined entity reference is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance. Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XQuery are as follows:
| Entity Reference | Character Represented |
< | < |
> | > |
& | & |
" | " |
' | ' |
A string literal may also contain a character reference. [Definition:] A character reference is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal code point. For example, the Euro symbol (€) can be represented by the character reference €. Character references are normatively defined in Section 4.1 of the XML specification (it is ·implementation-defined· whether the rules in [XML 1.0] or [XML 1.1] apply.)
Here are some examples of literal expressions:
data server software 
"12.5" denotes the string containing the characters '1', '2', '.', and
'5'.12 denotes the xs:integer value twelve.12.5 denotes the xs:decimal value twelve and one half.125E2 denotes the xs:double value twelve thousand, five hundred."He said, ""I don't like it.""" denotes a string containing two quotation marks and one apostrophe."Ben & Jerry's" denotes the xs:string value "Ben & Jerry's"."€99.50" denotes the xs:string value "€99.50".The xs:boolean values true and false can be represented by calls to the ·built-in functions·fn:true() and fn:false(), respectively.
Values of other atomic types can be constructed by calling the ·constructor function· for the given type. The constructor functions for XML Schema built-in types are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:
xs:integer("12") returns the integer value twelve.xs:date("2001-08-25") returns an item whose type is xs:date and whose value represents the date 25th August 2001.xdt:dayTimeDuration("PT5H") returns an item whose type is xdt:dayTimeDuration and whose value represents a duration of five hours.Constructor functions can also be used to create special values that have no literal representation, as in the following examples:
xs:float("NaN") returns the special floating-point value, "Not a Number."xs:double("INF") returns the special double-precision value, "positive infinity."It is also possible to construct values of various types by using a cast expression. For example:
9 cast as
hatsize returns the atomic value 9
whose type is hatsize.
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[Definition:] A variable reference is a QName preceded by a $-sign. Two variable references are equivalent if their local names are the same and their namespace prefixes are bound to the same namespace URI in the ·statically known namespaces·. An unprefixed variable reference is in no namespace.
Every variable reference must match a name in the ·in-scope variables·, which include variables from the following sources:
typeswitch expressions (3.12.2 Typeswitch). Function calls also bind values to the formal parameters of functions before executing the function body. Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a ·static error· [err:XPST0008]. to reference a variable that is not in scope. If a variable is bound in the ·static context· for an expression, that variable is in scope for the entire expression.
If a variable reference matches two or more variable bindings that are in scope, then the reference is taken as referring to the inner binding, that is, the one whose scope is smaller. At evaluation time, the value of a variable reference is the value of the expression to which the relevant variable is bound. The scope of a variable binding is defined separately for each kind of expression that can bind variables.
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Parentheses may be used to enforce a particular evaluation order in
expressions that contain multiple operators. For example, the expression (2 + 4)
* 5 evaluates to thirty, since the parenthesized expression (2 + 4) is evaluated first and its result is multiplied by five. Without
parentheses, the expression 2 + 4 * 5 evaluates to twenty-two, because the multiplication operator has higher
precedence than the addition operator.
Empty parentheses are used to denote an empty sequence, as described in 3.3.1 Constructing Sequences.
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A context item expression evaluates to
the ·context item·, which may be either a node (as in the
expression
fn:doc("bib.xml")/books/book[fn:count(./author)>1])
or an atomic value (as in the expression (1 to
100)[. mod 5 eq 0]).
If the ·context item· is undefined, a context item expression raises a dynamic error [err:XPDY0002]. .
[Definition:] The built-in functions supported by XQuery are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].Additional functions may be declared in a ·Prolog·, imported from a ·library module·, or provided by the external environment as part of the ·static context·.
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A function call consists of a QName followed by a parenthesized list of zero or more expressions, called arguments. If the QName in the function call has no namespace prefix, it is considered to be in the ·default function namespace.·
If the ·expanded QName· and number of arguments in a function call do not match the name and arity of a ·function signature· in the ·static context·, a ·static error· is raised [err:XPST0017]. .
A function call is evaluated as follows:
$p of type
xs:decimal can be invoked with an
argument of type xs:integer, which is
derived from xs:decimal. During the
processing of this function invocation, the ·dynamic
type· of $p inside the body of the
function is considered to be
xs:integer. Similarly, the value
returned by a function retains its most specific
type, which may be derived from the declared return
type of the function. For example, a function that
has a declared return type of
xs:decimal may in fact return a value
of dynamic type xs:integer.During evaluation of a function body, the ·static context· and ·dynamic context· for expression evaluation are defined by the ·module· in which the function is declared, which is not necessarily the same as the ·module· in which the function is called. For example, the variables in scope while
evaluating a function body are defined by in-scope variables of the
module that declares the function rather than the module in which the
function is called. During
evaluation of a function body, the ·focus·
(context item, context position, and context size) is
undefined, except where it is defined by some expression inside the function body.The function conversion rules are used to convert an argument value or a return value to its expected type; that is, to the declared type of the function parameter or return. The expected type is expressed as a ·sequence type·. The function conversion rules are applied to a given value as follows:
*,
+, or ?), the following
conversions are applied:xdt:untypedAtomic is cast to the expected
atomic type. For ·built-in functions· where the expected type is specified as ·numeric·, arguments of type xdt:untypedAtomic are cast to xs:double.xs:anyURI
in the atomic sequence that can be
·promoted· to the expected atomic type
using URI promotion as described in B.1 Type Promotion, the promotion is
done.Since the arguments of a function call are separated by commas, any argument expression that contains a top-level ·comma operator· must be enclosed in parentheses. Here are some illustrative examples of function calls:
my:three-argument-function(1,
2, 3) denotes a function call with three arguments.my:two-argument-function((1,
2), 3) denotes a function call with two arguments, the first of which is a
sequence of two values.my:two-argument-function(1,
()) denotes a function call with two arguments, the second of which is an
empty sequence.my:one-argument-function((1, 2,
3)) denotes a function call with one argument that is a sequence of three
values. my:one-argument-function(( )) denotes a function call with one argument that is an empty sequence.my:zero-argument-function( ) denotes a function call with zero arguments.
3.2 Path Expressions
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[Definition:] A path expression can be used to locate nodes
within trees. A path expression consists of a series of one or more
·steps·, separated by "/" or
"//", and optionally beginning with
"/" or "//". An initial
"/" or "//" is an abbreviation for
one or more initial steps that are implicitly added to the
beginning of the path expression, as described below.
A path expression consisting of a single step is evaluated as described in 3.2.1 Steps.
A "/"
at the beginning of a path expression is an abbreviation for
the initial step fn:root(self::node()) treat as
document-node()/ (however, if the
"/" is the entire path expression, the trailing "/" is omitted from the expansion.) The effect
of this initial step is to begin the path at the root node of
the tree that contains the context node. If the context item
is not a node, a ·type
error· is raised
[err:XPTY0020].
. At
evaluation time, if the root node above the context node is
not a document node, a ·dynamic error· is
raised
[err:XPDY0050].
.
A "//" at the beginning of a path expression
is an abbreviation for the initial steps
fn:root(self::node()) treat as
document-node()/descendant-or-self::node()/ (however, "//" by itself is not a valid path expression
[err:XPST0003].
.) The
effect of these initial steps is to establish an initial node
sequence that contains the root of the tree in which the
context node is found, plus all nodes descended from this
root.
This node sequence is used as the input to subsequent steps
in the path expression. If the context item is not a node, a
·type error· is
raised
[err:XPTY0020].
. At evaluation time, if the
root node above the context node is not a document node, a
·dynamic error· is
raised
[err:XPDY0050].
.
Each
non-initial occurrence of "//" in a path expression is
expanded as described in 3.2.4 Abbreviated Syntax, leaving a
sequence of steps separated by "/". This sequence
of steps is then evaluated from left to right. Each operation
E1/E2 is evaluated as follows:
Expression E1 is evaluated,
and if the result is not a (possibly empty) sequence of nodes, a ·type error· is raised
[err:XPTY0019].
. Each node resulting from the evaluation of
E1 then serves in turn to provide an inner
focus for an evaluation of E2, as
described in 2.1.2 Dynamic Context. The sequences resulting from all the evaluations of E2 are combined as follows:
E2 returns a (possibly empty) sequence of
nodes, these sequences are combined, and duplicate nodes are eliminated
based on node identity. If ·ordering mode· is ordered, the resulting node sequence is returned in ·document
order·; otherwise it is returned in ·implementation-dependent· order.E2 returns a (possibly empty) sequence of
atomic values, these sequences are concatenated and returned. If ·ordering mode· is ordered, the returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2; otherwise the order of the returned sequence is ·implementation-dependent·.E2 return at least
one node and at least one atomic value, a ·type
error· is raised
[err:XPTY0018].
.As an example of a path expression, child::div1/child::para selects the
para element children of the div1
element children of the context node, or, in other words, the
para element grandchildren of the context node
that have div1 parents.
/" character can be used either as a complete path expression or as the beginning of a longer path expression such as "/*". Also, "*" is both the multiply operator and a wildcard in path expressions. This can cause
parsing difficulties when "/" appears on the left hand side of "*". This is resolved using the leading-lone-slash constraint. For example, "/*" and "/ *" are valid path
expressions containing wildcards, but "/*5" and "/ * 5" raise syntax errors. Parentheses must be used when
"/" is used on the left hand side of an operator,
as in "(/) * 5". Similarly, "4 + / * 5" raises a syntax error, but "4 + (/) * 5" is a valid expression. The expression "4 + /" is also valid, because / does not occur on the left hand side of the operator.
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[Definition:] A step is a part of a ·path expression· that generates a sequence of items and then filters the sequence by zero or more ·predicates·. The value of the step consists of those items that satisfy the predicates. A step may be either an ·axis step· or a ·filter expression·. Filter expressions are described in 3.3.2 Filter Expressions.
[Definition:] An axis step returns a sequence of nodes that are reachable from the context node via a specified axis. Such a step has two parts: an
axis, which defines the "direction of
movement" for the step, and a ·node test·,
which selects nodes based on their kind, name, and/or
·type annotation·. If the context item is a node, an axis
step returns a sequence of zero or more
nodes; otherwise, a ·type error· is
raised
[err:XPTY0020].
. If ·ordering mode· is ordered, the resulting node sequence is returned in ·document
order·; otherwise it is returned in ·implementation-dependent· order. An axis step may be either a forward
step or a reverse step, followed
by zero or more ·predicates·.
In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 3.2.4 Abbreviated Syntax.
The unabbreviated syntax for an axis step consists of the axis name
and node test separated by a double colon. The result of the step consists of the nodes
reachable from the context node via the specified axis that have the node kind, name,
and/or ·type annotation· specified by the node test. For example, the
step child::para selects the para element children of the context node: child is the name of the axis, and para is the name of the element nodes to be selected on this axis. The available axes are described in 3.2.1.1 Axes. The
available node tests are described in 3.2.1.2 Node Tests. Examples of
steps are provided in 3.2.3 Unabbreviated Syntax and 3.2.4 Abbreviated Syntax.
XQuery supports the following axes (subject to limitations as described in 5.2.4 Full Axis Feature):
child axis
contains the children of the context
node, which are the nodes returned by
the dm:children accessor
in [XQuery/XPath Data Model (XDM)]. descendant
axis is defined as the transitive closure of
the child axis; it contains the descendants
of the context node (the children, the children of the children, and so on)parent
axis contains the sequence
returned by the
dm:parent
accessor in [XQuery/XPath Data Model (XDM)], which returns
the parent of the context
node, or an empty sequence
if the context node has no
parentancestor axis is
defined as the transitive
closure of the parent axis; it
contains the ancestors of the
context node (the parent, the
parent of the parent, and so
on)following-sibling
axis contains the context node's following
siblings, those children of the context
node's parent that occur after the context
node in ·document order·; if the context node
is an attribute node, the
following-sibling axis is
emptypreceding-sibling
axis contains the context node's preceding
siblings, those children of the context
node's parent that occur before the context
node in ·document order·; if the context node
is an attribute node, the
preceding-sibling axis is
emptyfollowing axis
contains all nodes that are
descendants of the root of the tree in
which the context node is found, are
not descendants of the context node,
and occur after the context node in
·document order·preceding axis
contains all nodes that are
descendants of the root of the tree in
which the context node is found, are
not ancestors of the context node, and
occur before the context node in
·document order·attribute axis
contains the attributes of the context node,
which are the nodes returned by the
dm:attributes accessor in
[XQuery/XPath Data Model (XDM)]; the axis will be
empty unless the context node is an
elementself axis contains just the context node itselfdescendant-or-self axis contains the context node and the descendants of the context
nodeancestor-or-self axis contains the context node and the ancestors of the context node;
thus, the ancestor-or-self axis will always include the root nodeAxes can be categorized as forward axes and reverse axes. An axis that only ever contains the context node or nodes that are after the context node in ·document order· is a forward axis. An axis that only ever contains the context node or nodes that are before the context node in ·document order· is a reverse axis.
The parent, ancestor, ancestor-or-self, preceding, and preceding-sibling axes are reverse axes; all other axes are forward axes. The ancestor, descendant, following, preceding and self axes partition a document (ignoring attribute nodes):
they do not overlap and together they contain all the nodes in the
document.
[Definition:] Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain. Thus:
In a sequence of nodes selected by an axis step, each node is assigned a context position that corresponds to its position in the sequence. If the axis is a forward axis, context positions are assigned to the nodes in ·document order·, starting with 1. If the axis is a reverse axis, context positions are assigned to the nodes in ·reverse document order·, starting with 1. This makes it possible to select a node from the sequence by specifying its position.
child::para[1] selects the
first para element that is a child of the context node.
[Definition:] A node test is a condition that must be true for each node selected by a ·step·. The condition may be based on the kind of the node (element, attribute, text, document, comment, or processing instruction), the name of the node, or (in the case of element, attribute, and document nodes), the ·type annotation· of the node.
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[Definition:] A node test that consists only of a QName or a
Wildcard is called a name test. A name
test is true if and only if the kind of
the node is the ·principal node kind· for the step axis and the
·expanded QName· of the node is equal (on a codepoint basis) to the
·expanded QName· specified by the name test. For
example, child::para
selects the para element children of
the context node; if the context node has no
para children, it selects an empty set
of nodes. attribute::abc:href selects
the attribute of the context node with the QName
abc:href; if the context node has no
such attribute, it selects an empty set of
nodes.
A QName in a name test is resolved into an ·expanded QName· using the ·statically known namespaces· in the expression context. It is a ·static error· [err:XPST0008]. if the QName has a prefix that does not correspond to any statically known namespace. An unprefixed QName, when used as a name test on an axis whose ·principal node kind· is element, has the namespace URI of the ·default element/type namespace· in the expression context; otherwise, it has no namespace URI.
A name test is not satisfied by an element node whose name does not match the ·expanded QName· of the name test, even if it is in a ·substitution group· whose head is the named element.
A node test * is true for any node of the ·principal node kind· of the step axis. For example, child::* will select all element children of the context node, and attribute::* will select all attributes of the context node.
A node test can have the form
NCName:*. In this case, the prefix is
expanded in the same way as with a QName, using the
·statically known
namespaces· in the ·static context·. If
the prefix is not found in the statically known namespaces,
a ·static
error· is raised
[err:XPST0008].
.
The node test is true for any node of the ·principal
node kind· of the step axis whose ·expanded QName· has the namespace URI
to which the prefix is bound, regardless of the
local part of the name.
A node test can also
have the form *:NCName. In this case,
the node test is true for any node of the ·principal
node kind· of the step axis whose local name matches the given NCName,
regardless of its namespace or lack of a namespace.
[Definition:] An alternative form of a node test called a kind test can select nodes based on their kind, name, and ·type annotation·. The syntax and semantics of a kind test are described in 2.5.3 SequenceType Syntax and 2.5.4 SequenceType Matching. When a kind test is used in a ·node test·, only those nodes on the designated axis that match the kind test are selected. Shown below are several examples of kind tests that might be used in path expressions:
node()
matches any
node.text() matches
any text
node.comment()
matches any comment
node.element()
matches any element
node.schema-element(person)
matches any element node whose name is
person (or is in the ·substitution group·
headed by person), and whose type
annotation is the same as (or is derived from) the declared type of the person
element in the ·in-scope element declarations·.element(person) matches any element node whose name is
person, regardless of its type annotation.element(person, surgeon) matches any non-nilled element node whose name
is person, and whose type
annotation is
surgeon or is derived from surgeon.element(*,
surgeon) matches any non-nilled element node whose type
annotation is surgeon (or is derived from surgeon), regardless of
its
name.attribute() matches any
attribute node.attribute(price) matches
any attribute whose name is price,
regardless of its type annotation.attribute(*,
xs:decimal) matches any attribute whose type
annotation is xs:decimal (or is derived from xs:decimal), regardless of
its
name.document-node()
matches any document
node.document-node(element(book))
matches any document node whose content consists of
a single element node that satisfies the ·kind test·element(book), interleaved with zero or more
comments and processing
instructions.
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[Definition:] A predicate consists of an expression, called a predicate
expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others. For each item in the sequence to be filtered, the predicate expression is evaluated using an
inner focus derived from that item, as described in
2.1.2 Dynamic Context. The result of the predicate expression is
coerced to a xs:boolean value, called the predicate truth value, as
described below. Those items for which the predicate truth value is true are retained, and those for which the predicate truth value is false are discarded.
The predicate truth value is derived by applying the following rules, in order:
true if the value of the predicate expression is equal (by the eq operator) to the context position, and is false otherwise. [Definition:] A predicate whose predicate expression returns a numeric type is called a numeric predicate.unordered, the result of a numeric predicate is nondeterministic, as explained in 3.9 Ordered and Unordered Expressions.Here are some examples of ·axis steps· that contain predicates:
chapter element that is a child
of the context node:child::chapter[2]
"toy" and whose color
attribute has the value "red":descendant::toy[attribute::color = "red"]
employee children of the context node
that have both a secretary child element and an assistant child element:child::employee[secretary][assistant]
When using ·predicates· with a sequence of nodes selected using a
reverse axis, it is important to remember that the the
context positions for such a sequence are assigned in ·reverse
document order·. For example, preceding::foo[1]
returns the first qualifying foo element in ·reverse document order·, because the predicate is part of an ·axis step· using a reverse axis. By
contrast, (preceding::foo)[1] returns the first qualifying foo
element in ·document order·, because the parentheses cause (preceding::foo) to be parsed as a ·primary expression· in which context positions are assigned in document order. Similarly, ancestor::*[1]
returns the nearest ancestor element, because the ancestor axis is a
reverse axis, whereas (ancestor::*)[1] returns the root element (first ancestor in document order).
This section provides a number of examples of path expressions in which the axis is explicitly specified in each ·step·. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 3.2.4 Abbreviated Syntax.
child::para selects
the para element children of the context nodechild::* selects all element children of the context nodechild::text() selects all text node children of the context nodechild::node() selects all the children of the context node. Note that no attribute nodes are returned, because attributes are not children.attribute::name selects the name attribute of the context nodeattribute::* selects all the attributes of the context nodeparent::node() selects the parent of the context node. If the context node is an attribute node, this expression returns the element node (if any) to which the attribute node is attached.descendant::para selects the para element descendants of the context nodeancestor::div selects all div ancestors of the context nodeancestor-or-self::div selects the div ancestors of the context node and, if the context node is a div element, the context node as welldescendant-or-self::para selects the para element descendants of the context node and, if the context node is a para element, the context node as wellself::para selects the context node if it is a para element, and otherwise returns an empty sequencechild::chapter/descendant::para selects the para element
descendants of the chapter element children of the context nodechild::*/child::para selects all para grandchildren of the context node/ selects the root of the tree that contains the context node, but raises a dynamic error if this root is not a document node/descendant::para selects all the para elements in the same document as the context node/descendant::list/child::member selects all
the member elements that have a list parent and that are in the same document as the context nodechild::para[fn:position() = 1] selects the first para child of the context nodechild::para[fn:position() = fn:last()] selects the last para child of the context nodechild::para[fn:position() = fn:last()-1] selects the last but one para child of the context nodechild::para[fn:position() > 1] selects all the para children of the context node other than the first para child of the context nodefollowing-sibling::chapter[fn:position() = 1]selects the next chapter sibling of the context nodepreceding-sibling::chapter[fn:position() = 1]selects the previous chapter sibling of the context node/descendant::figure[fn:position() = 42] selects the forty-second figure element in the document containing the context node/child::book/child::chapter[fn:position() = 5]/child::section[fn:position() = 2] selects the
second section of the fifth chapter of the book whose parent is the document node that contains the context nodechild::para[attribute::type eq "warning"]selects
all para children of the context node that have a type attribute with value warningchild::para[attribute::type eq 'warning'][fn:position() = 5]selects the fifth para child of the context node that has a type attribute with value warningchild::para[fn:position() = 5][attribute::type eq "warning"]selects the fifth para child of the context node if that child has a type attribute with value warningchild::chapter[child::title = 'Introduction']selects
the chapter children of the context node that have one or
more title children whose ·typed value· is equal to the
string Introductionchild::chapter[child::title] selects the chapter children of the context node that have one or more title childrenchild::*[self::chapter or self::appendix]
selects the chapter and appendix children of the context nodechild::*[self::chapter or
self::appendix][fn:position() = fn:last()] selects the
last chapter or appendix child of the context node
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The abbreviated syntax permits the following abbreviations:
attribute:: can be
abbreviated by @. For example, a path expression para[@type="warning"] is short
for child::para[attribute::type="warning"] and
so selects para children with a type attribute with value
equal to warning.child unless the axis step contains an AttributeTest; in that case, the default axis is attribute. For example, the path expression section/para is an abbreviation for child::section/child::para, and the path expression section/@id is an abbreviation for child::section/attribute::id. Similarly, section/attribute(id) is an abbreviation for child::section/attribute::attribute(id). Note that the latter expression contains both an axis specification and a ·node test·.// is effectively replaced by /descendant-or-self::node()/ during processing of a path expression. For example, div1//para is
short for child::div1/descendant-or-self::node()/child::para and so will select all para descendants of div1 children.//para[1] does not mean the same as the path
expression /descendant::para[1]. The latter selects the first descendant para element; the former
selects all descendant para elements that are the first para children of their respective parents... is short
for parent::node(). For example, ../title is short for parent::node()/child::title and so will select the title children of the parent of the context node.., known as a context item
expression, is a ·primary expression·,
and is described in 3.1.4 Context Item Expression.Here are some examples of path expressions that use the abbreviated syntax:
para selects the para element children of the context node* selects all element children of the context nodetext() selects all text node children of the context node@name selects
the name attribute of the context node@* selects all the attributes of the context nodepara[1] selects the first para child of the context nodepara[fn:last()] selects the last para child of the context node*/para selects
all para grandchildren of the context node/book/chapter[5]/section[2] selects the
second section of the fifth chapter of the book whose parent is the document node that contains the context nodechapter//para selects the para element descendants of the chapter element children of the context node//para selects all
the para descendants of the root document node and thus selects all para elements in the same document as the context node//@version selects all the version attribute nodes that are in the same document as the context node//list/member selects all the member elements in the same document as the context node that have a list parent.//para selects
the para element descendants of the context node.. selects the parent of the context node../@lang selects
the lang attribute of the parent of the context nodepara[@type="warning"] selects all para children of the context node that have a type attribute with value warningpara[@type="warning"][5] selects the fifth para child of the context node that has a type attribute with value warningpara[5][@type="warning"] selects the fifth para child of the context node if that child has a type attribute with value warningchapter[title="Introduction"] selects the chapter children of the context node that have one
or more title children whose ·typed value· is equal to the string Introductionchapter[title] selects the chapter children of the context node that have one or more title childrenemployee[@secretary and @assistant] selects all
the employee children of the context node that have both a secretary attribute and
an assistant attributebook/(chapter|appendix)/section selects
every section element that has a parent that is either a chapter or an appendix element, that in turn is a child of a book element that is a child of the context node.E is any expression that returns a sequence of nodes, then the expression E/. returns the same nodes in ·document order·, with duplicates eliminated based on node identity. 3.3 Sequence ExpressionsXQuery supports operators to construct, filter, and combine
·sequences· of ·items·.
Sequences are never nested—for
example, combining the values 1, (2, 3), and ( ) into a single sequence results
in the sequence (1, 2, 3).
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[Definition:] One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence. Empty parentheses can be used to denote an empty sequence.
A sequence may contain duplicate atomic values or nodes, but a sequence is never an item in another sequence. When a new sequence is created by concatenating two or more input sequences, the new sequence contains all the items of the input sequences and its length is the sum of the lengths of the input sequences.
Here are some examples of expressions that construct sequences:
(10, 1, 2, 3, 4)
10, 1, 2, 3, 4.(10, (1, 2), (), (3, 4))
salary children of the context node followed by all bonus children.(salary, bonus)
$price is bound to
the value 10.50, the result of this expression is the sequence 10.50, 10.50.($price, $price)
A range expression can be used to construct a sequence of consecutive
integers. Each of the operands of the to operator is
converted as though it was an argument of a function with the expected
parameter type xs:integer?.
If either operand is an empty sequence, or if the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence. If the two operands convert to the same integer, the result of the range expression is that integer. Otherwise, the result is a sequence containing the two integer operands and
every integer between the two operands, in increasing order.
10, 1, 2, 3, 4.(10, 1 to 4)
10.10 to 10
15 to 10
fn:reverse function to construct a sequence of six integers in decreasing order. It evaluates to the sequence 15, 14, 13, 12, 11, 10.fn:reverse(10 to 15)
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[Definition:] A filter expression consists simply of a primary expression followed by zero or more ·predicates·. The result of the filter expression consists of all the items returned by the primary expression for which all the predicates are true. If no predicates are specified, the result is simply the result of the primary expression. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression. Context positions are assigned to items based on their ordinal position in the result sequence. The first context position is 1.
Here are some examples of filter expressions:
$products[price gt 100]
to operator.)(1 to 100)[. mod 5 eq 0]
(21 to 29)[5]
$book:$book/(chapter | appendix)[fn:last()]
tiger:fn:doc("zoo.xml")/fn:id('tiger')
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XQuery provides the following operators for combining sequences of nodes:
union and | operators are equivalent. They take two node sequences as operands and
return a sequence containing all the nodes that occur in either of the
operands.intersect operator takes two node sequences as operands and returns a sequence
containing all the nodes that occur in both operands.except operator takes two node sequences as operands and returns a sequence
containing all the nodes that occur in the first operand but not in the second
operand.
All these operators eliminate duplicate nodes from their result sequences based on node identity. If ·ordering mode· is ordered, the resulting sequence is returned in ·document
order·; otherwise it is returned in ·implementation-dependent· order.
If an operand
of union, intersect, or except contains an item that is not a node, a ·type error· is raised
[err:XPTY0004].
.
Here are some examples of expressions that combine sequences. Assume the existence of three element nodes that we will refer to by symbolic names A, B, and C. Assume that the variables $seq1, $seq2 and $seq3 are bound to the following sequences of these nodes:
$seq1 is bound to (A, B)$seq2 is bound to (A, B)$seq3 is bound to (B, C)Then:
$seq1 union $seq2 evaluates to the sequence (A, B). $seq2 union $seq3 evaluates to the sequence (A, B, C). $seq1 intersect $seq2 evaluates to the sequence (A, B). $seq2 intersect $seq3 evaluates to the sequence containing B only.$seq1 except $seq2 evaluates to the empty sequence.$seq2 except $seq3 evaluates to the sequence containing A only.In addition to the sequence operators described here, [XQuery 1.0 and XPath 2.0 Functions and Operators] includes functions for indexed access to items or sub-sequences of a sequence, for indexed insertion or removal of items in a sequence, and for removing duplicate items from a sequence.
3.4 Arithmetic ExpressionsXQuery provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.
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A subtraction operator must be preceded by whitespace if
it could otherwise be interpreted as part of the previous token. For
example, a-b will be interpreted as a
name, but a - b and a -b will be interpreted as arithmetic expressions. (See A.2.4 Whitespace Rules for further details on whitespace handling.)
The first step in evaluating an arithmetic expression is to evaluate its operands. The order in which the operands are evaluated is ·implementation-dependent·.
Each operand is evaluated by applying the following steps, in order:
xdt:untypedAtomic, it is cast to xs:double. If
the cast fails, a ·dynamic
error· is raised. [err:FORG0001]After evaluation of the operands, if the types of the operands are a valid combination for the given arithmetic operator, the operator is applied to the operands, resulting in an atomic value or a ·dynamic error· (for example, an error might result from dividing by zero.) The combinations of atomic types that are accepted by the various arithmetic operators, and their respective result types, are listed in B.2 Operator Mapping together with the ·operator functions· that define the semantics of the operator for each type combination, including the dynamic errors that can be raised by the operator. The definitions of the operator functions are found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a ·type error· is raised [err:XPTY0004]. .
XQuery supports two division operators named div and idiv. Each of these operators accepts two operands of any ·numeric· type. As described in [XQuery 1.0 and XPath 2.0 Functions and Operators], $arg1 idiv $arg2 is equivalent to ($arg1 div $arg2) cast as xs:integer? except for error cases.
Here are some examples of arithmetic expressions:
xs:decimal value -1.5, and the second expression returns the xs:integer value -1:-3 div 2 -3 idiv 2
xdt:dayTimeDuration:$emp/hiredate - $emp/birthdate
$unit-price - $unit-discount
-$bellcost + $whistlecost -($bellcost + $whistlecost)
3.5 Comparison ExpressionsComparison expressions allow two values to be compared. XQuery provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.
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The value comparison operators are eq, ne, lt, le, gt, and ge. Value comparisons are used for comparing single values.
The first step in evaluating a value comparison is to evaluate its operands. The order in which the operands are evaluated is ·implementation-dependent·. Each operand is evaluated by applying the following steps, in order:
xdt:untypedAtomic, it is cast to xs:string.xdt:untypedAtomic operands. Users should also be aware that transitivity of value comparisons may be compromised by loss of precision during type conversion (for example, two xs:integer values that differ slightly may both be considered equal to the same xs:float value because xs:float has less precision than xs:integer).After evaluation of the operands, if the types of the operands are a valid combination for the given operator, the operator is applied to the operands. The combinations of atomic types that are accepted by the various value comparison operators, and their respective result types, are listed in B.2 Operator Mapping together with the ·operator functions· that define the semantics of the operator for each type combination. The definitions of the operator functions are found in [XQuery 1.0 and XPath 2.0 Functions and Operators].
Informally, if both atomized operands consist of exactly one atomic
value, then the result of the comparison is true if the value of the
first operand is (equal, not equal, less than, less than or equal,
greater than, greater than or equal) to the value of the second
operand; otherwise the result of the comparison is false.
If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a ·type error· is raised [err:XPTY0004]. .
Here are some examples of value comparisons:
$book/author. The comparison is true only if the result of atomization is the value "Kennedy" as an instance of xs:string or xdt:untypedAtomic. If the result of atomization is an empty sequence, the result of the comparison is an empty sequence. If the result of atomization is a sequence containing more than one value, a ·type error· is raised
[err:XPTY0004].
.$book1/author eq "Kennedy"
weight subelement, the value of the predicate is the empty sequence, and the product is not selected://product[weight gt 100]
<a>5</a> eq <a>5</a>
<a>5</a> eq <b>5</b>
my:hatsize and my:shoesize are both user-defined types that are derived by restriction from a primitive ·numeric· type:my:hatsize(5) eq my:shoesize(5)
The general comparison operators are =, !=, <, <=, >, and >=. General comparisons are existentially quantified comparisons that may be applied to operand sequences of any length. The result of a general comparison that does not raise an error is
always true or false.
A general comparison is evaluated by applying the following rules, in order:
true if and only if there is a pair of
atomic values, one in the first operand sequence and the other in the second operand sequence, that have the required
magnitude relationship. Otherwise the result of the comparison is
false. The magnitude relationship between two atomic values is determined by
applying the following rules. If a cast operation called for by these rules is not successful, a dynamic error is raised. [err:FORG0001]x < 17 is a numeric comparison if x is an untyped value. Users should be aware that the value comparison operators have different rules for casting of xdt:untypedAtomic operands.xdt:untypedAtomic and the other is an instance of a ·numeric· type, then the xdt:untypedAtomic value is cast to the type xs:double.xdt:untypedAtomic and the other is an instance of xdt:untypedAtomic or xs:string, then the xdt:untypedAtomic value (or values) is (are) cast to the type xs:string.xdt:untypedAtomic and the other is not an instance of xs:string, xdt:untypedAtomic, or any ·numeric· type, then the xdt:untypedAtomic value is
cast to the ·dynamic type· of the other value.eq, ne, lt, le, gt, or
ge, depending on whether the general comparison operator was =, !=, <, <=,
>, or >=. The values have the required magnitude relationship if and only if the result
of this value comparison is true.When evaluating a general comparison in which either operand is a sequence of items, an implementation may return true as soon as it finds an item in the first operand and an item in the second operand that have the required magnitude relationship. Similarly, a general comparison may raise a ·dynamic error· as soon as it encounters an error in evaluating either operand, or in comparing a pair of items from the two operands. As a result of these rules, the result of a general comparison is not deterministic in the presence of errors.
Here are some examples of general comparisons:
author subelement of $book1 is "Kennedy" as an instance of xs:string or xdt:untypedAtomic:$book1/author = "Kennedy"
true, and the value of the third comparison is false. This example illustrates the fact that general comparisons are not transitive.(1, 2) = (2, 3) (2, 3) = (3, 4) (1, 2) = (3, 4)
true. This example illustrates the fact that the = and != operators are not inverses of each other.(1, 2) = (2, 3) (1, 2) != (2, 3)
$a, $b, and $c are bound to element nodes with type annotation xdt:untypedAtomic, with ·string values· "1", "2", and "2.0" respectively. Then ($a, $b) = ($c, 3.0) returns false, because $b and $c are compared as strings. However, ($a, $b) = ($c, 2.0) returns true, because $b and 2.0 are compared as numbers.Node comparisons are used to compare two nodes, by their identity or by their ·document order·. The result of a node comparison is defined by the following rules:
is operator is true if the two operand nodes have the same identity, and are thus the same node; otherwise it
is false. See [XQuery/XPath Data Model (XDM)] for a definition of node identity.<< operator returns true if the left operand node precedes the right operand node in
·document order·; otherwise it returns false.>> operator returns true if the left operand node follows the right operand node in
·document order·; otherwise it returns false.Here are some examples of node comparisons:
/books/book[isbn="1558604820"] is /books/book[call="QA76.9 C3845"]
<a>5</a> is <a>5</a>
/transactions/purchase[parcel="28-451"] << /transactions/sale[parcel="33-870"]
3.6 Logical ExpressionsA logical expression is either an and-expression or
an or-expression. If a logical expression does not raise an error, its value is always one
of the boolean values true or false.
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The first step in evaluating a logical expression is to find the ·effective boolean value· of each of its operands (see 2.4.3 Effective Boolean Value).
The value of an and-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:
| AND: | EBV2 =
true | EBV2 = false | error in EBV2 |
EBV1 =
true | true | false | error |
EBV1
= false | false | false | either false or
error |
| error in EBV1 | error | either false or
error | error |
The value of an or-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:
| OR: | EBV2 =
true | EBV2 = false | error in EBV2 |
EBV1 =
true | true | true | either true or
error |
EBV1 =
false | true | false | error |
| error in EBV1 | either true or
error | error | error |
The
order in which the operands of a logical expression are evaluated is
·implementation-dependent·. The tables above are defined in such a way
that an or-expression can return true if the first
expression evaluated is true, and it can raise an error if evaluation
of the first expression raises an error. Similarly, an and-expression
can return false if the first expression evaluated is
false, and it can raise an error if evaluation of the first expression
raises an error. As a result of these rules, a logical expression is
not deterministic in the presence of errors, as illustrated in the examples
below.
Here are some examples of logical expressions:
true:1 eq 1 and 2 eq 2
1 eq 1 or 2 eq 3
false or raise a ·dynamic error·:1 eq 2 and 3 idiv 0 = 1
true or raise a
·dynamic error·:1 eq 1 or 3 idiv 0 = 1
1 eq 1 and 3 idiv 0 = 1
In addition to and- and or-expressions, XQuery provides a
function named fn:not that takes a general sequence as
parameter and returns a boolean value. The fn:not function
is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The
fn:not function reduces its parameter to an ·effective boolean value·. It then returns
true if the effective boolean value of its parameter is
false, and false if the effective boolean
value of its parameter is true. If an error is
encountered in finding the effective boolean value of its operand,
fn:not raises the same error.
3.7 ConstructorsXQuery provides constructors that can create XML structures within a query. Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation, and computed constructors, which use a notation based on enclosed expressions.
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This section contains a conceptual description of the semantics of various kinds of constructor expressions. An XQuery implementation is free to use any implementation technique that produces the same result as the processing steps described in this section.
An element constructor creates an element node. [Definition:] A direct element constructor is a form of element constructor in which the name of the constructed element is a constant. Direct element constructors are based on standard XML notation. For example, the following expression is a direct element constructor
that creates a book element containing an attribute and some nested elements:
<book isbn="isbn-0060229357">
<title>Harold and the Purple Crayon</title>
<author>
<first>Crockett</first>
<last>Johnson</last>
</author>
</book>If the element name in a direct element constructor has a namespace prefix, the namespace prefix is resolved to a namespace URI using the ·statically known namespaces·. If the element name has no namespace prefix, it is implicitly qualified by the ·default element/type namespace·. Note that both the statically known namespaces and the default element/type namespace may be affected by ·namespace declaration attributes· found inside the element constructor. The namespace prefix of the element name is retained after expansion of the QName, as described in [XQuery/XPath Data Model (XDM)]. The resulting ·expanded QName· becomes the node-name property of the constructed element node.
In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix.
In a direct element constructor, curly braces { } delimit enclosed expressions, distinguishing them from literal text. Enclosed expressions are evaluated and replaced by their value, as illustrated by the following example:
<example>
<p> Here is a query. </p>
<eg> $b/title </eg>
<p> Here is the result of the query. </p>
<eg>{ $b/title }</eg>
</example>The above query might generate the following result (whitespace has been added for readability to this result and other result examples in this document):
<example> <p> Here is a query. </p> <eg> $b/title </eg> <p> Here is the result of the query. </p> <eg><title>Harold and the Purple Crayon</title></eg> </example>
Since XQuery uses curly braces to denote enclosed expressions, some
convention is needed to denote a curly brace used as an ordinary character. For
this purpose, a pair of identical curly brace characters within the content of an element or attribute are interpreted by XQuery as a single curly brace
character (that is, the pair "{{" represents the
character "{" and the pair "}}" represents
the character "}".) Alternatively, the ·character references·{ and } can be used to denote curly brace characters. A single left curly brace
("{") is interpreted as the beginning delimiter for an
enclosed expression. A single right curly brace ("}")
without a matching left curly brace is treated as a ·static error·
[err:XPST0003].
.
The result of an element constructor is a new element node, with its own node identity. All the attribute and descendant nodes of the new element node are also new nodes with their own identities, even if they are copies of existing nodes.
The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant QName, and the value of the attribute is specified by a string of characters enclosed in single or double quotes. As in the main content of the element constructor, an attribute value may contain expressions enclosed in curly braces, which are evaluated and replaced by their value during processing of the element constructor.
Each attribute in a direct element constructor creates a new attribute node, with its own node identity, whose parent is the constructed element node. However, note that ·namespace declaration attributes· (see 3.7.1.2 Namespace Declaration Attributes) do not create attribute nodes.
If an attribute name has a namespace prefix, the prefix is resolved to a namespace URI using the ·statically known namespaces·. If the attribute name has no namespace prefix, the attribute is in no namespace. Note that the statically known namespaces used in resolving an attribute name may be affected by ·namespace declaration attributes· that are found inside the same element constructor. The namespace prefix of the attribute name is retained after expansion of the QName, as described in [XQuery/XPath Data Model (XDM)]. The resulting ·expanded QName· becomes the node-name property of the constructed attribute node.
If the attributes in a direct element constructor do not have distinct ·expanded
QNames· as their respective node-name properties, a ·static error· is raised
[err:XPST0040].
.
Conceptually, an attribute (other than a namespace declaration attribute) in a direct element constructor is processed by the following steps:
string-value property of the attribute node. The attribute node is given a ·type annotation· (type-name property) of xdt:untypedAtomic (this type annotation may change if the parent element is validated). The typed-value property of the attribute node is the same as its string-value, as an instance of xdt:untypedAtomic.parent property of the attribute node is set to the element node constructed by the direct element constructor that contains this attribute.xml:id, the string value and typed value of the attribute are further normalized by discarding any leading and
trailing space (#x20) characters, and by replacing sequences of
space (#x20) characters by a single space (#x20) character.xml:id processing as defined in [XML ID].xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.<shoe size="7"/>The string value of the
size attribute is "7".<shoe size="{7}"/>The string value of the size attribute is "7".<shoe size="{()}"/>The string value of the size attribute is the zero-length string.<chapter ref="[{1, 5 to 7, 9}]"/>The string value of the ref attribute is "[1 5 6 7 9]".<shoe size="As big as {$hat/@size}"/>The string value of the size attribute is the
string "As big as ", concatenated with the string value of the
node denoted by the expression
$hat/@size.The names of a constructed element and its attributes may be ·QNames· that include namespace prefixes. Namespace prefixes can be bound to namespaces in the ·Prolog· or by namespace declaration attributes. It is a ·static error· to use a namespace prefix that has not been bound to a namespace [err:XPST0008]. .
[Definition:] A
namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the ·default element/type namespace· for the constructed element node, including its attributes. Syntactically, a namespace declaration attribute has the form of an attribute with namespace prefix xmlns, or with name xmlns and no namespace prefix. The value of a namespace declaration attribute must be a URILiteral; otherwise a ·static error· is raised
[err:XPST0022].
. All the namespace declaration attributes of a given element must have distinct names
[err:XPST0071].
. Each namespace declaration attribute is processed as follows:
xmlns with no prefix, the value of the attribute is interpreted as a namespace URI. This URI specifies the ·default element/type namespace· of the constructor expression (overriding any existing default), and is added (with no prefix) to the ·in-scope namespaces· of the constructed element (overriding any existing namespace binding with no prefix). If the namespace URI is a zero-length string, the ·default element/type namespace· of the constructor expression is set to "none," and any no-prefix namespace binding is removed from the ·in-scope namespaces· of the constructed element.xml or xmlns, or binds a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.A namespace declaration attribute does not cause an attribute node to be created.
The following examples illustrate namespace declaration attributes:
http://example.org/animals:<cat xmlns = "http://example.org/animals"> <breed>Persian</breed> </cat>
metric and english:<box xmlns:metric = "http://example.org/metric/units"
xmlns:english = "http://example.org/english/units">
<height> <metric:meters>3</metric:meters> </height>
<width> <english:feet>6</english:feet> </width>
<depth> <english:inches>18</english:inches> </depth>
</box>The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of text characters (parsed as ElementContentChar), nested direct constructors, CdataSections, character and ·predefined entity references·, and expressions enclosed in curly braces. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic values. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.
Conceptually, the content of an element constructor is processed as follows:
strip, ·boundary whitespace· is identified and deleted (see 3.7.1.4 Boundary Whitespace for a definition of boundary whitespace.)< and &, are treated as literal characters rather than as markup characters (except for the sequence ]]>, which terminates the CDataSection).parent property of the resulting node is then set to the newly constructed element node.parent, children, and attributes properties of the copied nodes are set so as to preserve their inter-node relationships. For the topmost node (the node directly returned by the enclosed expression), the parent property is set to the node constructed by this constructor.strip:type-name property is set to xdt:untyped. Its nilled, is-id, and is-idrefs properties are set to false.type-name property is set to xdt:untypedAtomic. Its is-idrefs property is set to false. Its is-id property is set to true if the qualified name of the attribute node is xml:id; otherwise it is set to false.string-value of each copied element and attribute node remains unchanged, and its typed-value becomes equal to its string-value as an instance of xdt:untypedAtomic.preserve, the type-name, nilled, string-value, typed-value, is-id, and is-idrefs properties of the copied nodes are preserved.in-scope-namespaces property of a copied element node is
determined by the following rules. In applying these rules, the default
namespace or absence of a default namespace is treated like any other
namespace binding:preserve, all in-scope-namespaces of the original element are
retained in the new copy. If ·copy-namespaces mode· specifies no-preserve, the new copy retains only those in-scope namespaces of the original element that are used in the names of the element and its
attributes. It is a
·type error·
[err:XPTY0086].
in this case if the ·typed value· of the copied element or of any of
its attributes is ·namespace-sensitive·. [Definition:] A value is namespace-sensitive if it
includes an item whose ·dynamic type· is xs:QName or xs:NOTATION or is
derived by restriction from xs:QName or xs:NOTATION.preserve,
since otherwise the typed value of the copied node is never namespace-sensitive.inherit, the copied node inherits all the in-scope namespaces of the constructed node, augmented and overridden by the in-scope namespaces of the original element that were preserved by the preceding rule. If ·copy-namespaces mode· specifies no-inherit, the copied node does not inherit any in-scope namespaces from the constructed node.base-uri
property is set to be the same as that of its new parent,
with the following exception: if a copied element node has an xml:base attribute, its base-uri property is set to
the value of that attribute, resolved (if it is relative) against
the base-uri property of the new parent node.node-name is the ·expanded QName· resulting from resolving the element name in the start tag, including its original namespace prefix (if any), as described in 3.7.1 Direct Element Constructors.base-uri is taken from the first of the following sources that exists:xml:base, if this attribute exists;parent is set to empty.attributes consist of all the attributes specified in the start tag as described in 3.7.1.1 Attributes, together with all the attribute nodes in the content sequence, in ·implementation-dependent· order. If two or more of these attributes have the same node-name, a ·dynamic error· is raised
[err:XPDY0025].
. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node.children consist of all the element, text, comment, and processing
instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.in-scope-namespaces consist of all the namespace bindings resulting from namespace declaration attributes as described in 3.7.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 3.7.4 In-scope Namespaces of a Constructed Element.nilled property is false.string-value property is equal to the concatenated contents of the text-node descendants in document order. If there are no text-node descendants, the string-value property is a zero-length string.typed-value property is equal to the string-value property, as an instance of xdt:untypedAtomic.strip, the type-name property is xdt:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.is-id and is-idrefs properties are set to false.<a>{1}</a>The constructed element node has one child, a text node containing the value "1".<a>{1, 2, 3}</a>The constructed element node has one child, a text node containing the value "1 2 3".<c>{1}{2}{3}</c>The constructed element node has one child, a text node containing the value "123".<b>{1, "2", "3"}</b>The constructed element node has one child, a text node containing the value "1 2 3".<fact>I saw 8 cats.</fact>The constructed element node has one child, a text node containing the value "
I saw 8 cats.".<fact>I saw {5 + 3} cats.</fact>The constructed element node has one child, a text node containing the value "I saw 8 cats.".<fact>I saw <howmany>{5 + 3}</howmany> cats.</fact>The constructed element node has three children: a text node containing "I saw ", a child element node named howmany, and a text node containing " cats.". The child element node in turn has a single text node child containing the value "8".In a direct element constructor, whitespace characters may appear in the content of the constructed element. In some cases, enclosed expressions and/or nested elements may be separated only by whitespace characters. For
example, in the expression below, the end-tag
</title> and the start-tag <author> are separated by a newline character and four space
characters:
<book isbn="isbn-0060229357">
<title>Harold and the Purple Crayon</title>
<author>
<first>Crockett</first>
<last>Johnson</last>
</author>
</book>[Definition:] Boundary whitespace is a
sequence of consecutive whitespace characters within the content of a ·direct element constructor·, that is delimited at each end either by the start or
end of the content, or by a DirectConstructor, or by an EnclosedExpr. For this purpose, characters generated by
·character references· such as   or by CdataSections are not
considered to be whitespace characters.
The ·boundary-space policy· in the ·static context· controls whether boundary whitespace is
preserved by element constructors. If boundary-space policy is strip, boundary whitespace is not considered significant and
is discarded. On the other hand, if boundary-space policy is preserve, boundary whitespace is
considered significant and is
preserved.
<cat>
<breed>{$b}</breed>
<color>{$c}</color>
</cat>The constructed
cat element node has two child element nodes named
breed and color. Whitespace surrounding
the child elements will be stripped away by the element
constructor if boundary-space policy is
strip.<a> {"abc"} </a>If
boundary-space policy is strip, this example is equivalent to <a>abc</a>. However, if
boundary-space policy is preserve, this example is
equivalent to <a> abc </a>.<a> z {"abc"}</a>Since the
whitespace surrounding the z is not boundary
whitespace, it is always preserved. This example is equivalent to
<a> z abc</a>.<a> {"abc"}</a>This
example is equivalent to <a> abc</a>, regardless
of the boundary-space policy, because the space generated by the ·character reference· is not treated as a whitespace character.<a>{" "}</a>This example constructs an element containing two space characters,
regardless of the boundary-space policy, because whitespace inside an enclosed expression is never considered to be boundary whitespace.xml:space as ordinary attributes. An xml:space attribute does not affect the handling of whitespace by an element constructor.XQuery allows an expression to generate a processing instruction node or a comment node. This can be accomplished by using a direct processing instruction constructor or a direct comment constructor. In each case, the syntax of the constructor expression is based on the syntax of a similar construct in XML.
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A direct processing instruction constructor creates a processing instruction node whose target property is PITarget and whose content property is DirPIContents. The base-uri property of the node is empty. The parent property of the node is empty.
The PITarget of a processing instruction may not consist of the characters "XML" in any combination of upper and lower case. The DirPIContents of a processing instruction may not contain the string "?>".
The following example illustrates a direct processing instruction constructor:
<?format role="output" ?>
A direct comment constructor creates a comment node whose content property is DirCommentContents. Its parent property is empty.
The DirCommentContents of a comment may not contain two consecutive hyphens or end with a hyphen. These rules are syntactically enforced by the grammar shown above.
The following example illustrates a direct comment constructor:
<!-- Tags are ignored in the following section -->
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An alternative way to create nodes is by
using a computed constructor. A
computed constructor begins with a keyword that identifies the type
of node to be created: element,
attribute, document, text, processing-instruction, or comment.
For those kinds of nodes that have names (element, attribute, and processing instruction nodes), the keyword that specifies the node kind is followed by the name of the node to be created. This name may be specified either as a QName or as an expression enclosed in braces. [Definition:] When an expression is used to specify the name of a constructed node, that expression is called the name expression of the constructor.
[Definition:] The final part of a computed constructor is an expression enclosed in braces, called the content expression of the constructor, that generates the content of the node.
The following example illustrates the use of computed element and attribute constructors in a simple case where the names of the constructed nodes are constants. This example generates exactly the same result as the first example in 3.7.1 Direct Element Constructors:
element book {
attribute isbn {"isbn-0060229357" },
element title { "Harold and the Purple Crayon"},
element author {
element first { "Crockett" },
element last {"Johnson" }
}
}
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[Definition:] A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.
If the keyword element is followed by a QName, it is expanded using the ·statically known namespaces·, and the resulting ·expanded QName· is used as the node-name property of the constructed element node. If expansion of the QName is not successful, a ·static error· is raised
[err:XPST0081].
.
If the keyword element is followed by a ·name expression·, the name expression is processed as follows:
xs:QName, xs:string, or xdt:untypedAtomic, a ·type
error· is raised
[err:XPTY0004].
.xs:QName, that ·expanded QName· is used as the node-name property of the constructed
element, retaining the prefix part of the QName.xs:string or xdt:untypedAtomic, that value is converted to an ·expanded QName·. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the ·statically known namespaces·. If the string value contains no namespace prefix, it is treated as a local name in the ·default element/type namespace·. The resulting ·expanded QName· is used as the node-name property of the constructed
element, retaining the prefix part of the QName. If conversion of the atomized ·name expression· to an expanded QName is not successful, a ·dynamic error· is raised
[err:XPDY0074].
.The ·content expression· of a computed element constructor (if present) is processed in exactly the same way as an enclosed expression in the content of a ·direct element constructor·, as described in Step 1e of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. If the ·content expression· is absent, the content sequence is an empty sequence.
Processing of the computed element constructor proceeds as follows:
node-name is the ·expanded QName· resulting from processing the specified QName or ·name expression·, as described above.base-uri is taken from the first of the following sources that exists:xml:base, if this attribute exists;parent is empty.attributes consist of all the attribute nodes in the content sequence, in ·implementation-dependent· order. If two or more of these attributes have the same node-name, a ·dynamic error· is raised
[err:XPDY0025].
. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node.children consist of all the element, text, comment, and processing
instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.in-scope-namespaces are computed as described in 3.7.4 In-scope Namespaces of a Constructed Element.nilled property is false.string-value property is equal to the concatenated contents of the text-node descendants in document order.typed-value property is equal to the string-value property, as an instance of xdt:untypedAtomic.strip, the type-name property is xdt:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.is-id and is-idrefs properties are set to false.A computed element constructor might be
used to make a modified copy of an existing element. For example,
if the variable $e is bound to an element with ·numeric·
content, the following constructor might be used to create a new
element with the same name and attributes as $e and
with numeric content equal to twice the value of
$e:
element {fn:node-name($e)}
{$e/@*, 2 * fn:data($e)}In this example, if $e is
bound by the expression let $e := <length
units="inches">{5}</length>, then the result of the
example expression is the element <length
units="inches">10</length>.
fn:node-name($e) is xs:QName?, denoting zero or one QName. Therefore, if the ·Static Typing Feature· is in effect, the above example raises a static type error, since the name expression in a computed element constructor is required to return exactly one string or QName. In order to avoid the static type error, the name expression fn:node-name($e) could be rewritten as fn:exactly-one(fn:node-name($e)). If the ·Static Typing Feature· is not in effect, the example can be successfully evaluated as written, provided that $e is bound to exactly one element node with numeric content.One important
purpose of computed constructors is to allow the name of a node to
be computed. We will illustrate this feature by an expression that
translates the name of an element from one language to
another. Suppose that the variable $dict is bound to a
dictionary element containing a sequence of entry elements, each of which encodes translations for a specific word. Here is an example
entry that encodes the German and Italian variants of the word "address":
<entry word="address"> <variant xml:lang="de">Adresse</variant> <variant xml:lang="it">indirizzo</variant> </entry>
Suppose further that the variable $e is bound to the following element:
<address>123 Roosevelt Ave. Flushing, NY 11368</address>
Then the following expression generates a new element in which the name of $e has been translated into Italian and the content of $e (including its attributes, if any) has been preserved. The first enclosed expression after the element keyword generates the name of the element, and the second enclosed
expression generates the content and attributes:
element
{$dict/entry[@word=name($e)]/variant[@xml:lang="it"]}
{$e/@*, $e/node()}The result of this expression is as follows:
<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>
fn:exactly-one function in order to avoid a static type error.Additional examples of computed element constructors can be found in I.4 Recursive Transformations.
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A computed attribute constructor creates a new attribute node, with its own node identity.
If the keyword attribute is followed by a QName, that QName is expanded using the ·statically known namespaces·, and the resulting ·expanded QName· (including its prefix) is used as the node-name property of the constructed attribute node. If expansion of the QName is not successful, a ·static error· is raised
[err:XPST0081].
.
If the keyword attribute is followed by a ·name expression·, the name expression is processed as follows:
xs:QName, xs:string, or xdt:untypedAtomic, a ·type
error· is raised
[err:XPTY0004].
.xs:QName, that ·expanded QName· (including its prefix) is used as the node-name property of the constructed
attribute node.xs:string or xdt:untypedAtomic, that value is converted to an ·expanded QName·. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the ·statically known namespaces·. If the string value contains no namespace prefix, it is treated as a local name in no namespace. The resulting ·expanded QName· (including its prefix) is used as the node-name property of the constructed
attribute. If conversion of the atomized ·name expression· to an ·expanded QName· is not successful, a ·dynamic error· is raised
[err:XPDY0074].
.The node-name property of the constructed attribute (an ·expanded QName·) is checked as follows: If its URI part is http://www.w3.org/2000/xmlns/ (corresponding to namespace prefix xmlns) or if it is in no namespace and its local name is xmlns, a ·dynamic error·
[err:XPDY0044].
is raised.
The ·content expression· of a computed attribute constructor is processed as follows:
string-value property of the new attribute node. The ·type annotation· (type-name property) of the new attribute node is xdt:untypedAtomic. The typed-value property of the attribute node is the same as its string-value, as an instance of xdt:untypedAtomic.parent property of the attribute node is set to empty.xml:id, the string value and typed value of the attribute are further normalized by discarding any leading and
trailing space whitespace characters, and by replacing sequences of
whitespace characters by a single space (#x20) character.xml:id processing as defined in [XML ID].xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.attribute size {4 + 3}The ·string value· of the size attribute is "7" and its type is xdt:untypedAtomic.attribute
{ if ($sex = "M") then "husband" else "wife" }
{ <a>Hello</a>, 1 to 3, <b>Goodbye</b> }The name of the constructed attribute is either husband or wife. Its ·string value· is "Hello 1 2 3 Goodbye".
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All document node constructors are computed constructors. The result of a document node constructor is a new document node, with its own node identity.
A document node constructor is useful when the result of a query is to be a document in its own right. The following example illustrates a query that returns an XML document containing a root element named author-list:
document
{
<author-list>
{fn:doc("bib.xml")/bib/book/author}
</author-list>
}The ·content expression· of a document node constructor is processed in exactly the same way as an enclosed expression in the content of a ·direct element constructor·, as described in Step 1e of 3.7.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the document node constructor then proceeds as follows:
base-uri is taken from ·base URI· in the ·static context·. If no base URI is defined in the static context, the base-uri property is empty.children consist of all the element, text, comment, and processing
instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed document node.unparsed-entities and document-uri properties are empty.string-value property is equal to the concatenated contents of the text-node descendants in document order.typed-value property is equal to the string-value property, as an instance of xdt:untypedAtomic.No validation is performed on the constructed document node. The [XML 1.0] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.
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All text node constructors are computed constructors. The result of a text node constructor is a new text node, with its own node identity.
The ·content expression· of a text node constructor is processed as follows:
content property of the constructed text node.The parent property of the constructed text node is set to empty.
The following example illustrates a text node constructor:
text {"Hello"}
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A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity.
If the keyword processing-instruction is followed by an NCName, that NCName is used as the target property of the constructed node. If the keyword processing-instruction is followed by a ·name expression·, the name expression is processed as follows:
xs:NCName, xs:string, or xdt:untypedAtomic, a ·type
error· is raised
[err:XPTY0004].
.xs:string or xdt:untypedAtomic, that value is cast to the type xs:NCName. If the value cannot be cast to xs:NCName, a ·dynamic error· is raised
[err:XPDY0041].
.target property of the newly constructed processing instruction node. However, a ·dynamic error· is raised if the NCName is equal to "XML" (in any combination of upper and lower case)
[err:XPDY0064].
.The ·content expression· of a computed processing instruction constructor is processed as follows:
?>", a ·dynamic error·
[err:XPDY0026].
is raised.content property of the constructed processing instruction node.The remaining properties of the new processing instruction node are determined as follows:
parent property is empty.base-uri property is empty.The following example illustrates a computed processing instruction constructor:
let $target := "audio-output",
$content := "beep"
return processing-instruction {$target} {$content}The processing instruction node constructed by this example might be serialized as follows:
<?audio-output beep?>
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A computed comment constructor (CompCommentConstructor) constructs a new comment node with its own node identity. The ·content expression· of a computed comment constructor is processed as follows:
content property of the constructed comment node.The parent property of the constructed comment node is set to empty.
The following example illustrates a computed comment constructor:
let $homebase := "Houston"
return comment {fn:concat($homebase, ", we have a problem.")}The comment node constructed by this example might be serialized as follows:
<!--Houston, we have a problem.-->
An element node constructed by a direct or computed element constructor has an ·in-scope namespaces· property that consists of a set of ·namespace bindings·. The in-scope namespaces of an element node may affect the way the node is serialized (see 2.2.4 Serialization), and may also affect the behavior of certain functions that operate on nodes, such as fn:name. Note the difference between ·in-scope namespaces·, which is a dynamic property of an element node, and ·statically known namespaces·, which is a static property of an expression. Also note that one of the namespace bindings in the in-scope namespaces may have no prefix (denoting the default namespace for the given element). The in-scope namespaces of a constructed element node consist of the following namespace bindings:
xml to the namespace URI http://www.w3.org/XML/1998/namespace.The following query serves as an example:
declare namespace p="http://example.com/ns/p";
declare namespace q="http://example.com/ns/q";
declare namespace f="http://example.com/ns/f";
<p:a q:b="{f:func(2)}" xmlns:r="http://example.com/ns/r"/>
The ·in-scope namespaces· of the resulting p:a element consists of the following ·namespace bindings·:
p = "http://example.com/ns/p"q = "http://example.com/ns/q"r = "http://example.com/ns/r"
xml = "http://www.w3.org/XML/1998/namespace"The
namespace bindings for p and q are added to the result element because their respective namespaces
are used in the names of the element and its attributes. The namespace binding r="http://example.com/ns/r" is added to the in-scope namespaces of the constructed
element because it is defined by a ·namespace declaration attribute·, even though it is not used in a name.
No namespace binding corresponding to f="http://example.com/ns/f" is created, because the namespace prefix f appears only in the query prolog and is not used in an element or attribute name of the constructed node. This namespace binding does not appear in the query result, even though it is present in the ·statically known namespaces· and is available for use during processing of the query.
Note that the following constructed element, if nested within a validate expression, cannot be validated:
<p xsi:type="xs:integer">3</p>
The constructed element will have namespace bindings for the prefixes xsi (because it is used in a name) and xml (because it is defined for every constructed element node). During validation of the constructed element, the validator will be unable to interpret the namespace prefix xs because it is has no namespace binding. Validation of this constructed element could be made possible by providing a ·namespace declaration attribute·, as in the following example:
<p xmlns:xs="http://www.w3.org/2001/XMLSchema" xsi:type="xs:integer">3</p>
3.8 FLWOR ExpressionsXQuery provides a feature called a FLWOR expression that supports iteration and binding of variables to intermediate results. This
kind of expression is often useful for computing joins between two or more
documents and for restructuring data. The name FLWOR,
pronounced "flower", is suggested by the keywords for, let, where, order by, and return.
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The for and let clauses in a FLWOR expression generate an ordered sequence of tuples of bound variables, called the tuple stream. The optional where clause serves to filter the tuple stream, retaining some tuples and discarding others. The optional order by clause can be used to reorder the tuple stream. The return clause constructs the result of the FLWOR expression. The return clause is evaluated once for every tuple in the tuple stream, after filtering by the where clause, using the variable bindings in the respective tuples. The result of the FLWOR
expression is an ordered sequence containing the results of these
evaluations, concatenated as if by the ·comma operator·.
The following example of a FLWOR expression includes all of the possible clauses. The for clause iterates over all the departments in an input document, binding the variable $d to each department number in turn. For each binding of $d, the let clause binds variable $e to all the employees in the given department, selected from another input document. The result of the for and let clauses is a tuple stream in which each tuple contains a pair of bindings for $d and $e ($d is bound to a department number and $e is bound to a set of employees in that department). The where clause filters the tuple stream by keeping only those binding-pairs that represent departments having at least ten employees. The order by clause orders the surviving tuples in descending order by the average salary of the employees in the department. The return clause constructs a new big-dept element for each surviving tuple, containing the department number, headcount, and average salary.
for $d in fn:doc("depts.xml")/depts/deptno
let $e := fn:doc("emps.xml")/emps/emp[deptno = $d]
where fn:count($e) >= 10
order by fn:avg($e/salary) descending
return
<big-dept>
{
$d,
<headcount>{fn:count($e)}</headcount>,
<avgsal>{fn:avg($e/salary)}</avgsal>
}
</big-dept>The clauses in a FLWOR expression are described in more detail below.
The purpose of the for and let clauses in a FLWOR expression is to produce a tuple stream in which each tuple consists of one or more bound variables.
The simplest example of a for clause contains one variable and an associated expression. [Definition:] The value of the expression associated with a variable in a for clause is called the binding sequence for that variable. The for clause iterates over the items in the binding sequence, binding the variable to each item in turn. If ·ordering mode· is ordered, the resulting sequence of variable bindings is ordered according to the order of values in the binding sequence; otherwise the ordering of the variable bindings is ·implementation-dependent·.
A for clause may also contain multiple variables, each with an associated expression whose value is the binding sequence for that variable. In this case, the for clause iterates each variable over its binding sequence. The resulting tuple stream contains one tuple for each combination of values in the respective binding sequences. If ·ordering mode· is ordered, the order of the tuple stream is determined primarily by the order of the binding sequence of the leftmost variable, and secondarily by the binding sequences of the other variables, working from left to right. Otherwise, the ordering of the variable bindings is ·implementation-dependent·.
A let clause may also contain one or more variables, each with an associated expression. Unlike a for clause, however, a let clause binds each variable to the result of its associated expression, without iteration. The variable bindings generated by let clauses are added to the binding tuples generated by the for clauses. If there are no for clauses, the let clauses generate one tuple containing all the variable bindings.
Although for and let clauses both bind variables, the manner in which variables are bound is quite
different, as illustrated by the following examples. The first example uses a let clause:
let $s := (<one/>, <two/>, <three/>)
return <out>{$s}</out>The variable $s is bound to the result of the expression (<one/>,
<two/>, <three/>). Since there are no for clauses, the let clause generates one tuple that contains the binding of $s.
The return clause is invoked for this tuple, creating the following output:
<out> <one/> <two/> <three/> </out>
The next example is a similar query that contains a for clause instead of a let clause:
for $s in (<one/>, <two/>, <three/>)
return <out>{$s}</out>In this example, the variable $s iterates over the given expression. If ·ordering mode· is ordered, $s is first bound to <one/>, then to <two/>, and finally to <three/>. One tuple is generated for each of these bindings, and the return clause is invoked for each tuple, creating the following output:
<out> <one/> </out> <out> <two/> </out> <out> <three/> </out>
The following example illustrates how binding tuples are generated by a for clause that contains multiple variables when ·ordering mode· is ordered.
for $i in (1, 2), $j in (3, 4)
The tuple stream generated by the above for clause is as follows:
($i = 1, $j = 3) ($i = 1, $j = 4) ($i = 2, $j = 3) ($i = 2, $j = 4)
If ·ordering mode· were unordered, the for clause in the above example would generate the same tuple stream but the order of the tuples would be ·implementation-dependent·.
The scope of a variable bound in a for or let clause comprises all subexpressions of the containing FLWOR expression
that appear after the variable binding. The scope does not
include the expression to which the variable is bound. The following example illustrates how bindings in for and let clauses may reference variables that were bound in earlier clauses, or in earlier bindings in the same clause of the FLWOR expression:
for $x in $w, $a in f($x) let $y := g($a) for $z in p($x, $y) return q($x, $y, $z)
The for and let clauses of a given FLWOR expression may bind the same variable name more than once. In this case, each new binding occludes the previous one, which becomes inaccessible in the remainder of the FLWOR expression.
Each variable bound in a
for or let clause may have an optional
type declaration, which is a type declared using the
syntax in 2.5.3 SequenceType Syntax. If the type of a value bound to the variable does not match the declared type according to the rules for ·SequenceType
matching·, a ·type error· is raised
[err:XPTY0004].
. For example, the following expression raises a ·type error· because the variable $salary has a type declaration that is not satisfied by the value that is bound to the variable:
let $salary as xs:decimal := "cat" return $salary * 2
Each variable bound in a for clause may have an associated positional variable that is bound at the same time. The name of the positional variable is preceded by the keyword at. The positional variable always has an implied type of xs:integer. As a variable iterates over the items in its ·binding sequence·, its positional variable iterates over the integers that represent the ordinal positions of those items in the binding sequence, starting with 1.
Positional variables are illustrated by the following for clause:
for $car at $i in ("Ford", "Chevy"),
$pet at $j in ("Cat", "Dog")If ·ordering mode· is ordered, the tuple stream generated by the above for clause is as follows:
($i = 1, $car = "Ford", $j = 1, $pet = "Cat") ($i = 1, $car = "Ford", $j = 2, $pet = "Dog") ($i = 2, $car = "Chevy", $j = 1, $pet = "Cat") ($i = 2, $car = "Chevy", $j = 2, $pet = "Dog")
If ·ordering mode· is unordered, the order of the tuple stream is ·implementation-dependent·. In addition, if a for clause contains subexpressions that are affected by ·ordering mode·, the association of positional variables with items returned by these subexpressions is ·implementation-dependent· if ·ordering mode· is unordered.
The optional where clause serves as a filter for the tuples of variable bindings
generated by the for and let clauses. The expression in the where clause, called the where-expression, is evaluated once for
each of these tuples. If the ·effective boolean value· of the
where-expression is true, the tuple is retained and its variable bindings are used in an
execution of the return clause. If the ·effective boolean value· of the where-expression is false, the tuple is discarded. The ·effective boolean value· of an expression is defined in 2.4.3 Effective Boolean Value.
The following expression illustrates how a where clause might be applied to a positional variable in order to perform sampling on an input sequence. This expression approximates the average value in a sequence by sampling one value out of each one hundred input values.
fn:avg(for $x at $i in $inputvalues
where $i mod 100 = 0
return $x)The return clause of a FLWOR expression is evaluated once for each tuple in the tuple stream, and the results of these evaluations are concatenated, as if by the ·comma operator·, to form the result of the FLWOR expression.
If no order by clause is present, the order of the tuple stream is determined by the for and let clauses and by ·ordering mode·. If an order by clause is present, it reorders the tuples in the tuple stream into a new, value-based order. In either case, the resulting order determines the order in which the return clause is evaluated, once for each tuple, using the variable bindings in the respective tuples. Note that ·ordering mode· has no effect on a FLWOR expression if an order by clause is present, since order by takes precedence over ·ordering mode·.
An order by clause contains one or more ordering specifications, called orderspecs, as shown in the grammar above. For each tuple in the tuple stream, after filtering by the where clause, the orderspecs are evaluated, using the variable bindings in that tuple. The relative order of two tuples is determined by comparing the values of their orderspecs, working from left to right until a pair of unequal values is encountered. If an orderspec specifies a ·collation·, that collation is used in comparing values of type xs:string, xs:anyURI, or types derived from them (otherwise, the ·default collation· is used). If an orderspec specifies a collation by a relative URI, that relative URI is resolved to an absolute URI using the ·base URI· in the ·static context·. If an orderspec specifies a collation that is not found in ·statically known collations·, an error is raised
[err:XPST0076].
.
The process of evaluating and comparing the orderspecs is based on the following rules:
xdt:untypedAtomic (such as character
data in a schemaless document), it is cast to the type xs:string.gt operator. If two or more non-empty orderspec values are not convertible to a common type that has a gt operator, a ·type error· is raised
[err:XPTY0004].
.hatsize, which is derived from xs:integer, and a value of type shoesize, which is derived from xs:decimal. The least common type reachable by subtype substitution and type promotion is xs:decimal.xs:string and a value of type xs:anyURI. The least common type reachable by subtype substitution and type promotion is xs:string.When two orderspec values are compared to determine their relative position in the ordering sequence, the greater-than relationship is defined as follows:
empty least, a value W is considered to be greater-than a value V if one of the following is true:NaN, and W is neither NaN nor an empty sequence.gt V is true.fn:compare(V, W, C) is less than zero.empty greatest, a value W is considered to be greater-than a value V if one of the following is true:NaN, and V is neither NaN nor an empty sequence.gt V is true.fn:compare(V, W, C) is less than zero.empty least nor empty greatest, the ·default order for empty sequences· in the ·static context· determines whether the rules for empty least or empty greatest are used.If T1 and T2 are two tuples in the tuple stream, and V1 and V2 are the first pair of values encountered when evaluating their orderspecs from left to right for which one value is greater-than the other (as defined above), then:
descending, then T1 precedes T2 in the tuple stream; otherwise, T2 precedes T1 in the tuple stream.descending, then T2 precedes T1 in the tuple stream; otherwise, T1 precedes T2 in the tuple stream.If neither V1 nor V2 is greater-than the other for any pair of orderspecs for tuples T1 and T2, the following rules apply.
stable is specified, the original order of T1 and T2 is preserved in the tuple stream.stable is not specified, the order of T1 and T2 in the tuple stream is ·implementation-dependent·.+0.0 gt -0.0 and -0.0 gt +0.0 are both false.An order by clause makes it easy to sort the result of a FLWOR expression, even if the sort key is not included in the result of the expression. For example, the following expression returns employee names in descending order by salary, without returning the actual salaries:
for $e in $employees
order by $e/salary descending
return $e/nameorder by clause in a FLWOR expression is the only facility provided by XQuery for specifying a value ordering, a FLWOR expression must be used in some queries where iteration would not otherwise be necessary. For example, a list of books with price less than 100 might be obtained by a simple ·path expression· such as $books/book[price < 100]. But if these books are to be returned in alphabetic order by title, the query must be expressed as follows:for $b in $books/book[price < 100]
order by $b/title
return $bThe following example illustrates an order by clause that uses several options. It causes a collection of books to be sorted in primary order by title, and in secondary descending order by price. A specific ·collation· is specified for the title ordering, and in the ordering by price, books with no price are specified to occur last (as though they have the least possible price). Whenever two books with the same title and price occur, the keyword stable indicates that their input order is preserved.
for $b in $books/book
stable order by $b/title
collation "http://www.example.org/collations/fr-ca",
$b/price descending empty least
return $breturn clauses that contain comma operators,
since FLWOR expressions have a higher precedence than the comma
operator. For instance, the following query raises an error because
after the comma, $j is no longer within the FLWOR expression, and is an
undefined variable:let $i := 5,
$j := 20 * i
return $i, $jlet $i := 5,
$j := 20 * i
return ($i, $j)$j into the return clause of the FLWOR expression, as the
programmer probably intended:The following example illustrates how FLWOR expressions can be nested, and how ordering can be specified at multiple levels of an element hierarchy. The example query inverts a document hierarchy to
transform a bibliography into an author list. The input (bound to the variable $bib) is a bib element containing a list of
books, each of which in turn contains a list of authors. The example is based on
the following input:
<bib>
<book>
<title>TCP/IP Illustrated</title>
<author>Stevens</author>
<publisher>Addison-Wesley</publisher>
</book>
<book>
<title>Advanced Programming
in the Unix Environment</title>
<author>Stevens</author>
<publisher>Addison-Wesley</publisher>
</book>
<book>
<title>Data on the Web</title>
<author>Abiteboul</author>
<author>Buneman</author>
<author>Suciu</author>
</book>
</bib>The following query transforms the input document into a list in which each author's name appears only once, followed by a list of titles of books written by that author. The fn:distinct-values function is used to eliminate duplicates (by value) from a list of author nodes. The author list, and the lists of books published by each author, are returned in alphabetic order using the ·default collation·.
<authlist>
{
for $a in fn:distinct-values($bib/book/author)
order by $a
return
<author>
<name> {$a} </name>
<books>
{
for $b in $bib/book[author = $a]
order by $b/title
return $b/title
}
</books>
</author>
}
</authlist>The result of the above expression is as follows:
<authlist>
<author>
<name>Abiteboul</name>
<books>
<title>Data on the Web</title>
</books>
</author>
<author>
<name>Buneman</name>
<books>
<title>Data on the Web</title>
</books>
</author>
<author>
<name>Stevens</name>
<books>
<title>Advanced Programming
in the Unix Environment</title>
<title>TCP/IP Illustrated</title>
</books>
</author>
<author>
<name>Suciu</name>
<books>
<title>Data on the Web</title>
</books>
</author>
</authlist> 3.9 Ordered and Unordered Expressions
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The purpose of ordered and unordered expressions is to set the ·ordering mode· in the ·static context· to ordered or unordered for a certain region in a query. The specified ordering mode applies to the expression nested inside the curly braces. For expressions where the ordering of the result is not significant, a performance advantage may be realized by setting the ordering mode to unordered, thereby granting the system flexibility to return the result in the order that it finds most efficient.
·Ordering mode· affects the behavior of ·path expressions· that include a "/" or "//" operator or an ·axis step·; union, intersect, and except expressions; and FLWOR expressions that have no order by clause. If ordering mode is ordered, node sequences returned by path, union, intersect, and except expressions are in ·document order·; otherwise the order of these return sequences is ·implementation-dependent·. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions. Ordering mode has no effect on duplicate elimination.
unordered, certain functions that depend on the ordering of node sequences may return nondeterministic results. These functions include fn:position, fn:last, fn:index-of, fn:insert-before, fn:remove, fn:reverse, and fn:subsequence. Also, within a ·path expression· in an unordered region, ·numeric predicates· are nondeterministic. For example, in an ordered region, the path expression (//a/b)[5] will return the fifth qualifying b-element in ·document order·. In an unordered region, the same expression will return an ·implementation-dependent· qualifying b-element.The use of an unordered expression is illustrated by the following example, which joins together two documents named parts.xml and suppliers.xml. The example returns the part numbers of red parts, paired with the supplier numbers of suppliers who supply these parts. If an unordered expression were not used, the resulting list of (part number, supplier number) pairs would be required to have an ordering that is controlled primarily by the ·document order· of parts.xml and secondarily by the ·document order· of suppliers.xml. However, this might not be the most efficient way to process the query if the ordering of the result is not important. An XQuery implementation might be able to process the query more efficiently by using an index to find the red parts, or by using suppliers.xml rather than parts.xml to control the primary ordering of the result. The unordered expression gives the query evaluator freedom to make these kinds of optimizations.
unordered {
for $p in fn:doc("parts.xml")/parts/part[color = "Red"],
$s in fn:doc("suppliers.xml")/suppliers/supplier
where $p/suppno = $s/suppno
return
<ps>
{ $p/partno, $s/suppno }
</ps>
}In addition to ordered and unordered expressions, XQuery provides a function named fn:unordered that operates on any sequence of items and returns the same sequence in a nondeterministic order. A call to the fn:unordered function may be thought of as giving permission for the argument expression to be materialized in whatever order the system finds most efficient. The fn:unordered function relaxes ordering only for the sequence that is its immediate operand, whereas an unordered expression sets the ·ordering mode· for its operand expression and all nested expressions.
3.10 Conditional ExpressionsXQuery supports a conditional expression based on the keywords if, then, and else.
|
The expression following the if keyword is called the test expression, and the expressions
following the then and else keywords are called the then-expression and else-expression, respectively.
The first step in processing a conditional expression is to find the ·effective boolean value· of the test expression, as defined in 2.4.3 Effective Boolean Value.
The value of a conditional expression is defined as follows: If the
effective boolean value of the test expression is true, the value of the then-expression is returned. If the
effective boolean value of the test expression is false,
the value of the else-expression is returned.
Conditional expressions have a special rule for propagating ·dynamic errors·. If the effective value of the test expression is true, the conditional expression ignores (does not raise) any dynamic errors encountered in the else-expression. In this case, since the else-expression can have no observable effect, it need not be evaluated. Similarly, if the effective value of the test expression is false, the conditional expression ignores any ·dynamic errors· encountered in the then-expression, and the then-expression need not be evaluated.
Here are some examples of conditional expressions:
if ($widget1/unit-cost < $widget2/unit-cost) then $widget1 else $widget2
discounted, independently of its value:if ($part/@discounted) then $part/wholesale else $part/retail
3.11 Quantified ExpressionsQuantified expressions support existential and universal quantification. The
value of a quantified expression is always true or false.
|
A quantified expression begins with
a quantifier, which is the keyword some or every, followed by one or more in-clauses that are used to bind variables,
followed by the keyword satisfies and a test expression. Each in-clause associates a variable with an
expression that returns a sequence of items, called the binding sequence for that variable. The in-clauses generate tuples of variable bindings, including a tuple for each combination of items in the binding sequences of the respective variables. Conceptually, the test expression is evaluated for each
tuple of variable bindings. Results depend on the ·effective boolean value· of the test expressions, as defined in 2.4.3 Effective Boolean Value. The value of the quantified expression is defined
by the following rules:
some, the quantified expression is true if at least one evaluation of the test expression has the ·effective boolean value·true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding
tuples, the value of the quantified expression is false.every, the quantified expression is true if every evaluation of the test expression has the ·effective boolean value·true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding
tuples, the value of the quantified
expression is true.The scope of a variable bound in a quantified expression comprises all subexpressions of the quantified expression that appear after the variable binding. The scope does not include the expression to which the variable is bound.
Each variable bound in an in-clause of a quantified expression may have an optional type declaration. If the type of a value bound to the variable does not match the declared type according to the rules for ·SequenceType matching·, a ·type error· is raised [err:XPTY0004]. .
The order in which test expressions are evaluated for the various binding
tuples is ·implementation-dependent·. If the quantifier
is some, an implementation may
return true as soon as it finds one binding tuple for which the test expression has
an ·effective boolean value· of true, and it may raise a ·dynamic error· as soon as it finds one binding tuple for
which the test expression raises an error. Similarly, if the quantifier is every, an implementation may return false as soon as it finds one binding tuple for which the test expression has
an ·effective boolean value· of false, and it may raise a ·dynamic error· as soon as it finds one binding tuple for
which the test expression raises an error. As a result of these rules, the
value of a quantified expression is not deterministic in the presence of
errors, as illustrated in the examples below.
Here are some examples of quantified expressions:
true if every part element has a discounted attribute (regardless of the values of these attributes):every $part in /parts/part satisfies $part/@discounted
true if at least
one employee element satisfies the given comparison expression:some $emp in /emps/employee satisfies
($emp/bonus > 0.25 * $emp/salary)(1, 2, 3) and (2, 3, 4). The expression beginning with some evaluates to true, and the expression beginning with every evaluates to false.some $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4every $x in (1, 2, 3), $y in (2, 3, 4)
satisfies $x + $y = 4true or raise a ·type error·, since its test expression returns true for one variable binding
and raises a ·type error· for another:some $x in (1, 2, "cat") satisfies $x * 2 = 4
false or raise a ·type error·, since its test expression returns false for one variable binding and raises a ·type error· for another:every $x in (1, 2, "cat") satisfies $x * 2 = 4
true or raise a ·type error· during the ·dynamic evaluation
phase·.some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4
3.12 Expressions on SequenceTypesIn addition to their use in function parameters and results, ·sequence types· are used in instance of, typeswitch,cast, castable, and treat expressions.
|
The boolean
operator instance of
returns true if the value of its first operand matches
the SequenceType in its second
operand, according to the rules for ·SequenceType
matching·; otherwise it returns false. For example:
5 instance of xs:integerThis example returns true because the given value is an instance of the given type.5 instance of xs:decimalThis example returns true because the given value is an integer literal, and xs:integer is derived by restriction from xs:decimal.<a>{5}</a> instance of xs:integerThis example returns false because the given value is an element rather than an integer.(5, 6) instance of xs:integer+This example returns true because the given sequence contains two integers, and is a valid instance of the specified type.. instance of element()This example returns true if the context item is an element node or false if the context item is defined but is not an element node. If the context item is undefined, a ·dynamic error· is raised
[err:XPDY0002].
.
|
The typeswitch expression chooses one of several expressions to evaluate based on the ·dynamic type· of an input value.
In a typeswitch expression, the typeswitch keyword is followed by an expression enclosed in parentheses, called
the operand expression. This is the expression whose type is being
tested. The
remainder of the typeswitch expression consists of one or more case clauses and a default clause.
Each case clause specifies a SequenceType followed by a return expression. [Definition:] The effective case in a typeswitch expression is the first case clause such that the value of the operand expression matches the SequenceType in the case clause, using the rules of ·SequenceType
matching·. The value of the typeswitch expression is the value of the return expression in the effective case. If the value of the operand
expression does not match any SequenceType named in a case clause, the value of the typeswitch expression is the value of the return expression in the default clause.
In a case or default clause, if the value to be returned depends on the value of the operand expression, the clause must specify a variable name. Within the return expression of the case or default clause, this variable name is bound to the value of the operand expression. Inside a case clause, the ·static type· of the variable is the SequenceType named in the case clause. Inside a default clause, the static type of the variable is the same as the static type of the operand expression. If the value to be returned by a case or default clause does not depend on the value of the operand expression, the clause need not specify a variable.
The scope of a variable binding in a case or default clause comprises that clause. It is not an error for more than one case or default clause in the same typeswitch expression to bind variables
with the same name.
A special rule applies to propagation of ·dynamic errors· by typeswitch expressions. A typeswitch expression ignores (does not raise) any dynamic errors encountered in case clauses other than the ·effective case·. Dynamic errors encountered in the default clause are raised only if there is no ·effective case·.
The following example shows how a typeswitch expression might
be used to process an expression in a way that depends on its ·dynamic type·.
typeswitch($customer/billing-address)
case $a as element(*, USAddress) return $a/state
case $a as element(*, CanadaAddress) return $a/province
case $a as element(*, JapanAddress) return $a/prefecture
default return "unknown"
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Occasionally
it is necessary to convert a value to a specific datatype. For this
purpose, XQuery provides a cast expression that
creates a new value of a specific type based on an existing value. A
cast expression takes two operands: an input
expression and a target type. The type of the
input expression is called the input type. The target
type must be an atomic type that is in the ·in-scope schema types· and is not xs:NOTATION or xdt:anyAtomicType, optionally
followed by the occurrence indicator "?" to denote that an empty
sequence is permitted
[err:XPST0080].
. If the target type has no namespace prefix, it
is considered to be in the ·default element/type
namespace·. The semantics of the cast expression
are as follows:
? is specified after the target type, the result of the
cast expression is an empty sequence.? is not specified after the target type, a ·type error· is raised
[err:XPTY0004].
.cast is supported for the combinations of
input type and target type listed in . For each of these combinations, both
the input type and the target type are primitive ·schema types·. For
example, a value of type xs:string can be cast into the
schema type xs:decimal. For each of these built-in combinations,
the semantics of casting are specified in [XQuery 1.0 and XPath 2.0 Functions and Operators].If the target type of a cast expression is xs:QName, or is a type that is derived from xs:QName or xs:NOTATION, the input expression must be a string literal; otherwise a ·static error·
[err:XPST0083].
is raised.cast is
supported if the input type is a non-primitive atomic type that is derived by restriction from the target
type. In this case, the input value
is mapped into the value space of the target type, unchanged except
for its type. For example, if shoesize is derived by
restriction from xs:integer, a value of type
shoesize can be cast into the schema type
xs:integer.cast is
supported if the target type is a non-primitive atomic type and the input
type is xs:string or xdt:untypedAtomic. The
input value is first converted to a value in the lexical space of the
target type by applying the whitespace normalization rules for the
target type (as defined in [XML Schema]); a ·dynamic error· [err:FORG0001]
is raised if the resulting lexical value does not satisfy the pattern
facet of the target type. The lexical value is then converted to the
value space of the target type using the schema-defined rules for the
target type; a ·dynamic error· [err:FORG0001]
is raised if the resulting value does not satisfy all the facets of
the target type.cast is supported if
the target type is a non-primitive atomic type that is derived by restriction from the input type. The input value must satisfy all the
facets of the target type (in the case of the pattern facet, this is
checked by generating a string representation of the input value,
using the rules for casting to xs:string). The resulting
value is the same as the input value, but with a different ·dynamic type·.cast expression raises a ·type error·
[err:XPTY0004].
. If casting from the input type to the target type is supported but nevertheless it is not possible to cast the input value into the value space of the target type, a ·dynamic error· is raised. [err:FORG0001] This includes the case when any facet of the target type is not satisfied. For example, the expression "2003-02-31" cast as xs:date would raise a ·dynamic error·.
|
XQuery
provides an expression that tests whether a given value
is castable into a given target type. The target
type must be an atomic type that is in the ·in-scope schema types· and is not xs:NOTATION or xdt:anyAtomicType, optionally
followed by the occurrence indicator "?" to denote that an empty
sequence is permitted
[err:XPST0080].
. The expression V castable
as T returns true if the value V can
be successfully cast into the target type T by using a
cast expression; otherwise it returns
false. The castable expression can be used as a ·predicate· to
avoid errors at evaluation time. It can also be used to select an
appropriate type for processing of a given value, as illustrated in
the following example:
if ($x castable as hatsize) then $x cast as hatsize else if ($x castable as IQ) then $x cast as IQ else $x cast as xs:string
For every atomic type in the ·in-scope schema types· (except xs:NOTATION and xdt:anyAtomicType, which are not instantiable), a constructor function is implicitly defined. In each case, the name of the constructor function is the same as the name of its target type (including namespace). The signature of the constructor function for type
T is as follows:
T($arg as xdt:anyAtomicType?) as T?
[Definition:] The constructor function for a given type is used to convert instances of other atomic types into the given type. The semantics of the constructor function T($arg) are defined to be equivalent to the expression ($arg cast as T?).
The constructor functions for xs:QName and for types derived from xs:QName and xs:NOTATION require their arguments to be string literals; otherwise a static error
[err:XPST0083].
is raised. This rule is consistent with the semantics of cast expressions for these types, as defined in 3.12.3 Cast.
The following examples illustrate the use of constructor functions:
("2000-01-01" cast as
xs:date?).xs:date("2000-01-01")(($floatvalue * 0.2E-5) cast as xs:decimal?).xs:decimal($floatvalue * 0.2E-5)
xdt:dayTimeDuration value equal to 21 days. It is
equivalent to ("P21D" cast as xdt:dayTimeDuration?).xdt:dayTimeDuration("P21D")usa:zipcode is a user-defined atomic type
in the ·in-scope schema types·, then the
following expression is equivalent to the
expression ("12345" cast as
usa:zipcode?).usa:zipcode("12345")cast expression, if the ·default element/type
namespace· is "none". (See 4.13 Default Namespace Declaration for how to undeclare the ·default element/type
namespace·).17 cast as apple
apple(17)
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XQuery provides an
expression called treat that can be used to modify the
·static type· of its
operand.
Like cast, the treat
expression takes two operands: an expression and a SequenceType. Unlike
cast, however, treat does not change the
·dynamic type· or value of its operand. Instead, the purpose of
treat is to ensure that an expression has an expected
dynamic type at evaluation time.
The semantics of expr1 treat as type1 are as
follows:
treat expression is type1. This enables the
expression to be used as an argument of a function that requires a
parameter of type1.expr1 matches type1,
using the rules for ·SequenceType
matching·,
the treat expression returns the value of
expr1; otherwise, it raises a ·dynamic error·
[err:XPDY0050].
.
If the value of expr1 is returned, its identity is
preserved. The treat expression ensures that the value of
its expression operand conforms to the expected type at
run-time.$myaddress treat as element(*, USAddress)The ·static type· of
$myaddress may be element(*, Address), a
less specific type than element(*, USAddress). However,
at run-time, the value of $myaddress must match the type
element(*, USAddress) using rules for ·SequenceType
matching·;
otherwise a ·dynamic error· is
raised
[err:XPDY0050].
. 3.13 Validate Expressions
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A validate expression can be used to validate a document node or an element node with respect to the ·in-scope schema definitions·, using the schema validation process defined in [XML Schema]. If the operand of a validate expression does not evaluate to exactly one document or element node, a ·type error· is raised
[err:XPTY0030].
. In this specification, the node that is the operand of a validate expression is called the operand node.
A validate expression returns a new node with its own identity and with no parent. The new node and its descendants are given ·type annotations· that are generated by applying a validation process to the operand node. In some cases, default values may also be generated by the validation process.
A validate expression may optionally specify a validation mode. The default validation mode is strict. The result of a validate expression is defined by the following rules.
strict, then there must be a
top-level element declaration in the ·in-scope element declarations· that matches the root element information
item in the Infoset, and schema-validity assessment is
carried out using that declaration in accordance with item
2 of [XML Schema] Part 1, section 5.2, "Assessing Schema-Validity."
If there is no such element declaration, a ·dynamic error· is
raised
[err:XPDY0084].
.lax, then schema-validity
assessment is carried out in accordance with item
3 of [XML Schema] Part 1, section 5.2, "Assessing Schema-Validity."If validation mode is lax and the root element
information item has neither a top-level element
declaration nor an xsi:type attribute, [XML Schema] defines the recursive checking of children
and attributes as optional. During processing of an XQuery validate expression, this
recursive checking is required.xs:ENTITY or xs:ENTITIES.xs:NOTATION.xsi:type attributes on the elements being validated, and may generate new information items such as default attributes.validity property of the root element information item in the PSVI that results from the validation process.validity property of the root element information item is valid (for any validation mode), or if validation mode is lax and the validity property of the root element information item is notKnown, the PSVI is converted back into an ·XDM instance· as described in [XQuery/XPath Data Model (XDM)] Section 3.3, "Construction from a PSVI". The resulting node (a new node of the same kind as the operand node) is returned as the result of the validate expression.strict, the validated element must have a top-level element declaration in the effective schema, and must conform to this declaration. If validation mode is lax, the validated element must conform to its top-level element declaration if such a declaration exists in the effective schema. If validation mode
is lax and there is no top-level element declaration for the
element, and the element has an xsi:type attribute, then the
xsi:type attribute must name a top-level type definition in the
effective schema, and the element must conform to that type. The validated element corresponds either to the operand node or (if the operand node is a document node) to its element child.notKnown are converted into element nodes with ·type annotation·xs:anyType, and any attribute information items whose validity property is notKnown are converted into attribute nodes with ·type annotation·xdt:untypedAtomic, as described in . 3.14 Extension Expressions[Definition:] An extension expression is an expression whose semantics are ·implementation-defined·. Typically a particular extension will be recognized by some implementations and not by others. The syntax is designed so that extension expressions can be successfully parsed by all implementations, and so that fallback behavior can be defined for implementations that do not recognize a particular extension.
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An extension expression consists of one or more pragmas, followed by an expression enclosed in curly braces. [Definition:] A pragma is denoted by the delimiters (# and #), and consists of an identifying QName followed by ·implementation-defined· content. The content of a pragma may consist of any string of characters that does not contain the ending delimiter #). The QName of a
pragma must resolve to a namespace URI and local name, using the ·statically known namespaces·
[err:XPST0081].
.
Each implementation recognizes an ·implementation-defined· set of namespace URIs used to denote pragmas.
If the namespace part of a pragma QName is not recognized by the implementation as a pragma namespace, then the pragma is ignored. If all the pragmas in an ExtensionExpr are ignored, then the value of the ExtensionExpr is the value of the expression enclosed in curly braces; if this expression is absent, then a ·static error· is raised [err:XPST0079]. .
If an implementation recognizes the namespace of one or more pragmas in an ExtensionExpr, then the value of the ExtensionExpr, including its error behavior, is ·implementation-defined·. For example, an implementation that recognizes the namespace of a pragma QName, but does not recognize the local part of the QName, might choose either to raise an error or to ignore the pragma.
It is a ·static error· [err:XPST0013]. if an implementation recognizes a pragma but determines that its content is invalid.
If an implementation recognizes a pragma, it must report any static errors in the following expression even if it will not evaluate that expression (however, static type errors are raised only if the ·Static Typing Feature· is in effect.)
declare namespace exq = "http://example.org/XQueryImplementation";
(# exq:use-index #)
{ $bib/book/author[name='Berners-Lee'] }
An implementation that recognizes the exq:use-index pragma might use an
index to evaluate the expression that follows. An implementation that
does not recognize this pragma would evaluate the expression in its normal
way.xs:duration values using implementation-defined
semantics (this would normally be an error). Such changes to the language
semantics must be scoped to the expression contained within the curly
braces following the pragma.declare namespace exq = "http://example.org/XQueryImplementation";
for $x in
(# exq:distinct //city by @country #)
{ //city[not(@country = preceding::city/@country)] }
return f:show-city($x)
Here an implementation that recognizes the pragma will return the result of
evaluating the proprietary syntax exq:distinct //city by
@country,
while an implementation that does not recognize the pragma will instead
return the result of the expression //city[not(@country =
preceding::city/@country)]. If no fallback expression is required, or
if none is feasible, then the expression between the curly braces may be
omitted, in which case implementations that do not recognize the pragma will
raise a ·static error·.
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A query can be assembled from one or more fragments called modules. [Definition:] A module is a fragment of XQuery code that conforms to the Module grammar and can independently undergo the ·static analysis phase· described in 2.2.3 Expression Processing. Each module is either a ·main module· or a ·library module·.
[Definition:] A main module consists of a ·Prolog· followed by a ·Query Body·. A query has exactly one main module. In a main module, the ·Query Body· can be evaluated, and its value is the result of the query.
[Definition:] A module that does not contain a ·Query Body· is called a library module. A library module consists of a ·module declaration· followed by a ·Prolog·. A library module cannot be evaluated directly; instead, it provides function and variable declarations that can be imported into other modules.
The XQuery syntax does not allow a ·module· to contain both a ·module declaration· and a ·Query Body·.
[Definition:] A Prolog is a series of declarations and imports that define the processing environment for the ·module· that contains the Prolog. Each declaration or import is followed by a semicolon. A Prolog is organized into two parts.
The first part of the Prolog consists of setters, imports, namespace declarations, and default namespace declarations. [Definition:] Setters are declarations that set the value of some property that affects query processing, such as construction mode, ordering mode, or default collation. Namespace declarations and default namespace declarations affect the interpretation of QNames within the query. Imports are used to import definitions from schemas and modules. [Definition:] Each imported schema or module is identified by its target namespace, which is the namespace of the objects (such as elements or functions) that are defined by the schema or module.
The second part of the Prolog consists of declarations of variables, functions, and options. These declarations appear at the end of the Prolog because they may be affected by declarations and imports in the first part of the Prolog.
[Definition:] The Query Body, if present, consists of an expression that defines the result of the query. Evaluation of expressions is described in 3 Expressions. A module can be evaluated only if it has a Query Body.
4.1 Version Declaration
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[Definition:] Any ·module· may contain a version declaration. If present, the version declaration occurs at the beginning of the ·module· and identifies the applicable XQuery syntax and semantics for the ·module·. The version number "1.0" indicates a requirement that the ·module· must be processed by an implementation that supports XQuery Version 1.0. If the version declaration is not present, the version is presumed to be "1.0". An XQuery implementation must raise a ·static error· [err:XPST0031]. when processing a ·module· labeled with a version that the implementation does not support. It is the intent of the XQuery working group to give later versions of this specification numbers other than "1.0", but this intent does not indicate a commitment to produce any future versions of XQuery, nor if any are produced, to use any particular numbering scheme.
[Definition:] If present, a version declaration may optionally include an encoding declaration. The value of the string literal following the keyword encoding is an encoding
name, and must conform to the definition of EncName specified in [XML 1.0]
[err:XPST0087].
. The purpose of an encoding declaration is to allow the writer of a query to provide a string that indicates how the query is encoded, such as "UTF-8", "UTF-16", or "US-ASCII". Since the encoding of a query may change as the query moves from one environment to another, there can be no guarantee that the encoding declaration is correct.
The handling of an encoding declaration is ·implementation-dependent·. If an implementation has a priori knowledge of the encoding of a query, it may use this knowledge and disregard the encoding declaration. The semantics of a query are not affected by the presence or absence of an encoding declaration.
If a version declaration is present, no Comment may occur before the end of the version declaration. If such a Comment is present, the result is ·implementation-dependent·.
The following examples illustrate version declarations:
xquery version "1.0";
xquery version "1.0" encoding "utf-8";
4.2 Module Declaration
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[Definition:] A module declaration serves to identify a ·module· as a ·library module·. A module declaration begins with the keyword module and contains a namespace prefix and a URILiteral. The URILiteral identifies the ·target namespace· of the library module, which is the namespace for all variables and functions exported by the library module. The name of every variable and function declared in a library module must
have a namespace URI that is the same as the target namespace of the module; otherwise a ·static error· is raised
[err:XPST0048].
. In the ·statically known namespaces· of the library module, the namespace prefix specified in the module declaration is bound to the module's target namespace.
Any ·module· may import one or more library modules by means of a ·module import· that specifies the target namespace of the library modules to be imported. When a module imports one or more library modules, the variables and functions declared in the imported modules are added to the ·static context· and (where applicable) to the ·dynamic context· of the importing module.
The following is an example of a module declaration:
module namespace math = "http://example.org/math-functions";
4.3 Boundary-space Declaration
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[Definition:] A boundary-space declaration sets the ·boundary-space policy· in the ·static context·, overriding any implementation-defined default. Boundary-space policy controls whether ·boundary whitespace· is preserved by element constructors during processing of the query. If boundary-space policy is preserve, boundary whitespace is preserved. If boundary-space policy is strip, boundary whitespace is stripped (deleted). A further discussion of whitespace in constructed elements can be found in 3.7.1.4 Boundary Whitespace.
The following example illustrates a boundary-space declaration:
declare boundary-space preserve;
If a Prolog contains more than one boundary-space declaration, a ·static error· is raised [err:XPST0068]. .
4.4 Default Collation Declaration
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[Definition:] A default collation declaration sets the value of the ·default
collation· in the ·static context·, overriding any implementation-defined default. The default collation is the collation that is
used by functions and operators that require a collation
if no other collation is specified. For example, the
gt operator on strings is defined by a call to
the fn:compare function, which takes an optional
collation parameter. Since the gt operator does
not specify a collation, the fn:compare function
implements gt by using the default collation.
If neither the implementation nor the Prolog
specifies a default collation, the Unicode codepoint collation
(http://www.w3.org/2005/xpath-functions/collation/codepoint)
is used.
The following example illustrates a default collation declaration:
declare default collation "http://example.org/languages/Icelandic";
If a default collation declaration specifies a collation by a relative URI, that relative URI is resolved to an absolute URI using the ·base URI· in the ·static context·. If a Prolog contains more than one default collation declaration, or the value specified by a default collation declaration (after resolution of a relative URI, if necessary) is not present in ·statically known collations·, a ·static error· is raised [err:XPST0038]. .
4.5 Base URI Declaration
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[Definition:] A base URI declaration specifies the
·base URI· property of the ·static context·, which
is used when resolving relative URIs within a
·module·. For example, the fn:doc
function resolves a relative URI using the base URI of the
calling module.
The following is an example of a base URI declaration:
declare base-uri "http://example.org";
If a Prolog contains more than one base URI declaration, a ·static error· is raised [err:XPST0032]. .
4.6 Construction Declaration
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[Definition:] A construction declaration sets the ·construction
mode· in the ·static
context·, overriding any implementation-defined default. The
construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xdt:untyped; all element nodes copied during node construction receive the type xdt:untyped, and all attribute nodes copied during node construction receive the type xdt:untypedAtomic.
The following example illustrates a construction declaration:
declare construction strip;
If a Prolog specifies more than one construction declaration, a ·static error· is raised [err:XPST0067]. .
4.7 Ordering Mode Declaration
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[Definition:] An ordering mode declaration sets the ·ordering mode· in the ·static context·, overriding any implementation-defined default. This ordering mode applies to all expressions in a ·module· (including both the ·Prolog· and the ·Query Body·, if any), unless overridden by an ordered or unordered expression.
·Ordering mode· affects the behavior of ·path expressions· that include a "/" or "//" operator or an ·axis step·; union, intersect, and except expressions; and FLWOR expressions that have no order by clause. If ordering mode is ordered, node sequences returned by path, union, intersect, and except expressions are in ·document order·; otherwise the order of these return sequences is ·implementation-dependent·. The effect of ordering mode on FLWOR expressions is described in 3.8 FLWOR Expressions.
The following example illustrates an ordering mode declaration:
declare ordering unordered;
If a Prolog contains more than one ordering mode declaration, a ·static error· is raised [err:XPST0065]. .
4.8 Empty Order Declaration
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[Definition:] An empty order declaration sets the ·default order for empty sequences· in the ·static context,· which controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression. An individual order by clause may override the default order for empty sequences by specifying empty greatest or empty least.
The following example illustrates an empty order declaration:
declare default order empty least;
If a Prolog contains more than one empty order declaration, a ·static error· is raised [err:XPST0069]. .
order by clause is present, and specifies how empty sequences are treated by the order by clause (unless overridden). An ·ordering mode declaration·, on the other hand, applies only in the absence of an order by clause. 4.9 Copy-Namespaces Declaration
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[Definition:] A copy-namespaces declaration sets the value of ·copy-namespaces mode· in the ·static context·, overwriting any implementation-defined default. Copy-namespaces mode controls the namespace bindings that are assigned when an existing element node is copied by an element constructor. Handling of namespace bindings by element constructors is described in 3.7.1 Direct Element Constructors.
The following example illustrates a copy-namespaces declaration:
declare copy-namespaces preserve, no-inherit;
If a Prolog contains more than one copy-namespaces declaration, a ·static error· is raised [err:XPST0055]. .
4.10 Schema Import
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[Definition:] A schema import imports the element declarations, attribute declarations, and type definitions from a schema into the ·in-scope schema definitions·. The schema to be imported is identified by its ·target namespace·. The schema import may bind a namespace prefix to the target namespace of the imported schema, or may declare that target namespace to be the ·default element/type namespace·. The schema import may also provide optional hints for locating the schema.
The first URILiteral in a schema import specifies the target namespace of the schema to be imported. The URILiterals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an implementation-dependent way. Multiple location hints might be used to indicate more than one possible place to look for the schema or multiple physical resources to be assembled to form the schema.
A schema import that specifies a zero-length string as target namespace is considered to import a schema that has no target namespace. Such a schema import may not bind a namespace prefix [err:XPST0057]. , but it may set the default element/type namespace to a zero-length string (representing "no namespace"), thus enabling the definitions in the imported namespace to be referenced. If the default element/type namespace is not set to "no namespace", there is no way to reference the definitions in an imported schema that has no target namespace.
It is a ·static error·
[err:XPST0058].
if more than one schema import in the same ·Prolog· specifies the same target namespace. It is a ·static error·
[err:XPST0059].
if the implementation is not able to process a schema import by finding a valid schema with the specified target namespace. It is a ·static error·
[err:XPST0035].
if multiple imported schemas, or multiple physical resources within one schema, contain definitions for the same name in the same symbol space (for example, two definitions for the same element name, even if the definitions are consistent). However, it is not an error to import the schema with target namespace http://www.w3.org/2001/XMLSchema (predeclared prefix xs), even though the built-in types defined in this schema are implicitly included in the ·in-scope schema types.·
It is a ·static error· [err:XPST0012]. if the set of definitions contained in all schemas imported by a Prolog do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema] Part 1--i.e., each definition must be valid, complete, and unique.
The following example imports a schema,
specifying both its target namespace and its location, and binding the
prefix soap to the target namespace:
import schema namespace soap="http://www.w3.org/2003/05/soap-envelope" at "http://www.w3.org/2003/05/soap-envelope/";
The following example imports a schema by specifying only its target namespace, and makes it the default element/type namespace:
import schema default element namespace "http://example.org/abc";
The following example imports a schema that has no target namespace, providing a location hint, and sets the default element/type namespace to "no namespace" so that the definitions in the imported schema can be referenced:
import schema default element namespace "" at "http://example.org/xyz.xsd";
The following example imports a schema that has no target namespace and sets the default element/type namespace to "no namespace". Since no location hint is provided, it is up to the implementation to find the schema to be imported.
import schema default element namespace "";
4.11 Module Import
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[Definition:] A module import imports the function declarations and variable declarations from one or more ·library modules· into the ·function signatures· and ·in-scope variables· of the importing ·module·. Each module import names a ·target namespace· and imports an ·implementation-defined· set of modules that share this target namespace. The module import may bind a namespace prefix to the target namespace, and it may provide optional hints for locating the modules to be imported.
The first URILiteral in a module import must be of nonzero length
[err:XPST0088].
, and specifies the target namespace of the modules to be imported. The URILiterals that follow the at keyword are optional location hints, and can be interpreted or disregarded in an ·implementation-defined· way.
It is a ·static error· [err:XPST0047]. if more than one module import in a ·Prolog· specifies the same target namespace. It is a ·static error· [err:XPST0059]. if the implementation is not able to process a module import by finding a valid module definition with the specified target namespace. It is a ·static error· if the name and arity of a function declared in an imported module is the same as the name and arity of a function declared in the importing module or in another imported module (even if the declarations are consistent) [err:XPST0034]. . It is a ·static error· if the ·expanded QName· of a variable declared in an imported module is the same as the ·expanded QName· of a variable declared in the importing module or in another imported module (even if the declarations are consistent) [err:XPST0049]. .
Each ·module· has its own ·static context·. A ·module import· imports only functions and variable declarations; it does not import other objects from the imported modules, such as ·in-scope schema definitions· or ·statically known namespaces·. Module imports are not transitive—that is, importing a module provides access only to function and variable declarations contained directly in the imported module. For example, if module A imports module B, and module B imports module C, module A does not have access to the functions and variables declared in module C.
A module may import its own target namespace (this is interpreted as importing an ·implementation-defined· set of other modules that share its target namespace.) However, it is a ·static error· [err:XPST0073]. if the graph of module imports contains a cycle (that is, if there exists a sequence of modules M1 ... Mn such that each Mi imports Mi+1 and Mn imports M1), unless all the modules in the cycle share a common namespace.
It is a ·static error· [err:XPST0036]. to import a module if the importing module's ·in-scope schema types· do not include definitions for the schema type names that appear in variable declarations, function parameters, or function returns found in the imported module.
To illustrate the above rules, suppose that a certain schema defines a type named triangle. Suppose that a library module imports the schema, binds its target namespace to the prefix geometry, and declares a function with the following ·function signature·: math:area($t as geometry:triangle) as xs:double. If a query wishes to use this function, it must import both the library module and the schema on which it is based. Importing the library module alone would not provide access to the definition of the type geometry:triangle used in the signature of the area function.
The following example illustrates a module import:
import module namespace math = "http://example.org/math-functions";
4.12 Namespace Declaration
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[Definition:] A namespace declaration declares a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of ·statically known namespaces·. The namespace declaration is in scope throughout the query in which it is declared, unless it is overridden by a ·namespace declaration attribute· in a ·direct element constructor·.
If the URILiteral part of a namespace declaration is a zero-length
string, any existing namespace binding for the given prefix is removed
from the ·statically known namespaces·. This feature provides a way to
remove predeclared namespace prefixes such as local.
The following query illustrates a namespace declaration:
declare namespace foo = "http://example.org"; <foo:bar> Lentils </foo:bar>
In the query result, the newly created node is in the namespace
associated with the namespace URI http://example.org.
Multiple declarations of the same namespace prefix in a ·Prolog· result in a ·static error· [err:XPST0033]. .
It is a ·static error· [err:XPST0008]. if an expression contains a QName with a namespace prefix that is not in the ·statically known namespaces·.
XQuery has several predeclared namespace prefixes that are present in the ·statically known namespaces· before each query is processed. These prefixes may be used without an explicit declaration. They may be overridden by ·namespace declarations· in a ·Prolog· or by ·namespace declaration attributes· on constructed elements (however, the prefix xml may not be redeclared, and no other prefix may be bound to the namespace URI associated with the prefix xml
[err:XPST0070].
). The predeclared namespace prefixes are as follows:
xml = http://www.w3.org/XML/1998/namespacexs = http://www.w3.org/2001/XMLSchemaxsi = http://www.w3.org/2001/XMLSchema-instancefn = http://www.w3.org/2005/xpath-functionsxdt = http://www.w3.org/2005/xpath-datatypeslocal = http://www.w3.org/2005/xquery-local-functions (see 4.15 Function Declaration.)Additional predeclared namespace prefixes may be added to the ·statically known namespaces· by an implementation.
The namespace prefix xmlns also has a special significance (it identifies a ·namespace declaration attribute·), and it may not be redeclared
[err:XPST0070].
.
When element or attribute names are compared, they are considered identical if the local parts and namespace URIs match on a codepoint basis. Namespace prefixes need not be identical for two names to match, as illustrated by the following example:
declare namespace xx = "http://example.org";
let $i := <foo:bar xmlns:foo = "http://example.org">
<foo:bing> Lentils </foo:bing>
</foo:bar>
return $i/xx:bingAlthough the namespace prefixes xx and foo differ, both are bound to the namespace URI "http://example.org". Since xx:bing and foo:bing have the same local name and the same namespace URI, they match. The
output of the above query is as follows.
<foo:bing xmlns:foo = "http://example.org"> Lentils </foo:bing>
4.13 Default Namespace Declaration
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Default namespace declarations can be used in a ·Prolog· to facilitate the use of unprefixed QNames. The following kinds of default namespace declarations are supported:
declare default element namespace "http://example.org/names";A default element/type namespace declaration may be overridden by a ·namespace declaration attribute· in a ·direct element constructor·.
http://www.w3.org/2005/xpath-functions (however, this default may be overridden by an implementation.)The
following example illustrates the declaration of a default
function namespace:declare default function namespace
"http://example.org/math-functions";The effect of declaring
a default function namespace is that all functions in the
default function namespace, including implicitly-declared
·constructor functions·, can be invoked without
specifying a namespace prefix. When a function call uses a
function name with no prefix, the local name of the function
must match a function (including
implicitly-declared ·constructor functions·) in the default
function namespace
[err:XPST0017].
.Unprefixed attribute names and variable names are in no namespace.
4.14 Variable Declaration
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A variable declaration adds the ·static type· of a variable to the ·in-scope variables·, and may also add a value for the variable to the ·variable values·. If the ·expanded QName· of the variable is the same as that of another variable in ·in-scope variables·, a ·static error· is raised [err:XPST0049]. .
If a variable declaration includes a type, that type is added to the ·static context· as the type of the variable. If a variable declaration includes an expression but not an explicit type, the type of the variable is inferred from static analysis of the expression and is added to the ·static context·. If a variable declaration includes both a type and an expression, the value returned by the expression must match the declared type according to the rules for ·SequenceType matching·; otherwise a ·type error· is raised [err:XPTY0004]. .
[Definition:] If a variable declaration includes an expression, the expression is called an initializing expression. The initializing expression for a given variable must be evaluated before the evaluation of any expression that references the variable. The ·static context· for an initializing expression includes all functions that are declared or imported anywhere in the ·Prolog·, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the variable that is being initialized. If an initializing expression cannot be evaluated because of a circularity (for example, it depends on a function that in turn depends on the value of the variable that is being initialized), a ·static error· is raised [err:XPST0054]. .
If the variable declaration
includes the keyword external, a value must be
provided for the variable by the external environment before
the query can be evaluated. If an external variable declaration also includes a declared type, the value provided by the external environment must match the declared type according to the rules for ·SequenceType
matching· (see 2.2.5 Consistency Constraints). If an external variable declaration does not include a declared type, the type and a matching value must be provided by the external environment at evaluation time. The ·static type· of such a variable is considered to be item()*.
All variable names declared in a ·library module· must (when expanded) be in the ·target namespace· of the library module [err:XPST0048]. . When a library module is imported, variables declared in the imported module are added to the ·in-scope variables· of the importing module.
Variable names that have no namespace prefix are in no namespace. Variable declarations that have no namespace prefix may appear only in a main module.
The term variable declaration always refers to a declaration of a variable in a ·Prolog·. The binding of a variable to a value in a query expression, such as a FLWOR expression, is known as a variable binding, and does not make the variable visible to an importing module.
Here are some examples of variable declarations:
xs:integer to be
associated with variable $x in the ·static context·, and the
value 7 to be associated with variable
$x in the ·dynamic
context·.declare variable $x as xs:integer := 7;
$x has a static type of
xs:decimal, inferred from its value which is
7.5.declare variable $x := 7.5;
external indicates that the value of the
variable will be provided by the external environment. At
evaluation time, if the variable $x in the
·dynamic context·
does not have a value of type xs:integer, a type
error is raised.declare variable $x as xs:integer external;
$x, whose type and value will be provided by the
external environment. During query analysis, the type of
$x is considered to be
item()*. During query evaluation, the
·dynamic context· must include a type and a value for $x, and its value must be compatible with its type.declare variable $x external;
declare variable $math:pi as xs:double := 3.14159E0;
4.15 Function DeclarationIn addition to the built-in functions described in [XQuery 1.0 and XPath 2.0 Functions and Operators], XQuery allows users to declare functions of their own. A function declaration specifies the name of the function, the names and datatypes of the parameters, and the datatype of the result. All datatypes are specified using the syntax described in 2.5 Types. A function declaration causes the declared function to be added to the ·function signatures· of the ·module· in which it appears.
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A function declaration specifies whether a function is ·user-defined· or ·external·. [Definition:] For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.. The ·static context· for a function body includes all functions that are declared or imported anywhere in the ·Prolog·, but it includes only those variables and namespaces that are declared or imported earlier in the Prolog than the function that is being defined.
[Definition:] External functions are functions that are implemented outside the query environment. For example, an XQuery implementation might provide a set of external functions in addition to the core function library described in [XQuery 1.0 and XPath 2.0 Functions and Operators]. External functions are identified by the keyword external. The purpose of a function declaration for an external function is to declare the datatypes of the function parameters and result, for use in type checking of the query that contains or imports the function declaration.
An XQuery implementation may provide a facility whereby external functions can be implemented using a host programming language, but it is not required to do so. If such a facility is provided, the protocols by which parameters are passed to an external function, and the result of the function is returned to the invoking query, are ·implementation-defined·. An XQuery implementation may augment the type system of
[XQuery/XPath Data Model (XDM)] with additional types that are designed to facilitate exchange of data with host programming
languages, or it may provide mechanisms for the user to define such
types. For example, a type might be provided that encapsulates an object returned by an
external function, such as an SQL database connection. These additional types, if defined, are considered to be derived
by restriction from xdt:anyAtomicType.
Every user-defined function must be in a namespace--that is, every declared function name must (when expanded) have a non-null namespace URI [err:XPST0060]. . If the function name in a function declaration has no namespace prefix, it is considered to be in the ·default function namespace·. Every function name declared in a ·library module· must (when expanded) be in the ·target namespace· of the library module [err:XPST0048]. . It is a ·static error· [err:XPST0045]. if the function name in a function declaration (when expanded) is in any of the following namespaces:
http://www.w3.org/XML/1998/namespacehttp://www.w3.org/2001/XMLSchemahttp://www.w3.org/2001/XMLSchema-instancehttp://www.w3.org/2005/xpath-functionshttp://www.w3.org/2005/xpath-datatypesIt is a ·static error· [err:XPST0034]. if the ·expanded QName· and arity (number of arguments) of the declared function are the same as the ·expanded QName· and arity of another function in ·function signatures·.
In order to allow main modules to declare functions for local use within the module without defining a new namespace, XQuery predefines the namespace prefix local to the namespace http://www.w3.org/2005/xquery-local-functions. It is suggested (but not required) that this namespace be used for defining local functions.
If a function parameter is declared using a name but no type, its default type is item()*. If the result type is omitted from a function declaration, its default result type is item()*.
The parameters of a function declaration are considered to be variables whose scope is the function body. It is an ·static error· [err:XPST0039]. for a function declaration to have more than one parameter with the same name. The type of a function parameter can be any type that can be expressed as a ·sequence type·.
The following example illustrates the declaration and use of a local function that
accepts a sequence of employee elements, summarizes them by department, and returns a sequence of dept elements.
declare function local:summary($emps as element(employee)*)
as element(dept)*
{
for $d in fn:distinct-values($emps/deptno)
let $e := $emps[deptno = $d]
return
<dept>
<deptno>{$d}</deptno>
<headcount> {fn:count($e)} </headcount>
<payroll> {fn:sum($e/salary)} </payroll>
</dept>
};
local:summary(fn:doc("acme_corp.xml")//employee[location = "Denver"])Rules for converting function arguments to their declared parameter types, and for converting the result of a function to its declared result type, are described in 3.1.5 Function Calls
A function declaration may be recursive—that is, it may reference itself. Mutually recursive functions, whose bodies reference each other,
are also allowed. The following example declares a recursive function that
computes the maximum depth of a node hierarchy, and calls the function to
find the maximum depth of a particular document. In its declaration, the
user-declared function local:depth calls the built-in functions empty and max, which are in the default function namespace.
partlist.xml.declare function local:depth($e as node()) as xs:integer
{
(: A node with no children has depth 1 :)
(: Otherwise, add 1 to max depth of children :)
if (fn:empty($e/*)) then 1
else fn:max(for $c in $e/* return local:depth($c)) + 1
};
local:depth(fn:doc("partlist.xml"))
Since a ·constructor function· is effectively declared for every user-defined atomic type in the ·in-scope schema types·, a ·static error· [err:XPST0034]. is raised if the Prolog attempts to declare a single-parameter function with the same ·expanded QName· as any of these types.
4.16 Option Declaration[Definition:] An option declaration declares an option that affects the behavior of a particular implementation. Each option consists of an identifying QName and a StringLiteral.
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Typically, a particular option will be recognized by some implementations and not by others. The syntax is designed so that option declarations can be successfully parsed by all implementations.
The QName of an option must resolve to a namespace URI and local name, using the ·statically known namespaces· [err:XPST0081]. .
Each implementation recognizes an ·implementation-defined· set of namespace URIs used to denote option declarations.
If the namespace part of the QName is not a namespace recognized by the implementation as one used to denote option declarations, then the option declaration is ignored.
Otherwise, the effect of the option declaration, including its error behavior, is ·implementation-defined·. For example, if the local part of the QName is not recognized, or if the StringLiteral does not conform to the rules defined by the implementation for the particular option declaration, the implementation may choose whether to report an error, ignore the option declaration, or take some other action.
Implementations may impose rules on where particular option declarations may appear relative to variable declarations and function declarations, and the interpretation of an option declaration may depend on its position.
An option declaration must not be used to change the syntax accepted by the processor, or to suppress the detection of static errors. However, it may be used without restriction to modify the semantics of the query. The scope of the option declaration is ·implementation-defined·—for example, an option declaration might apply to the whole query, to the current module, or to the immediately following function declaration.
The following examples illustrate several possible uses for option declarations:
declare namespace exq = "http://example.org/XQueryImplementation"; declare option exq:output "encoding = iso-8859-1";
fn:doc() function should be handled:declare option exq:strip-comments "true";
declare namespace math = "http://example.org/MathLibrary"; declare option exq:java-class "math = java.lang.Math";
This section defines the conformance criteria for an XQuery processor. In this section, the following terms are used to indicate the requirement levels defined in [RFC 2119]. [Definition:] MUST means that the item is an absolute requirement of the specification.[Definition:] MAY means that an item is truly optional.[Definition:] SHOULD means that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
An XQuery processor that claims to conform to this specification ·MUST· include a claim of Minimal Conformance as defined in 5.1 Minimal Conformance. In addition to a claim of Minimal Conformance, it ·MAY· claim conformance to one or more optional features defined in 5.2 Optional Features.
5.1 Minimal ConformanceMinimal Conformance to this specification ·MUST· include all of the following items:
5.2 Optional Features[Definition:] The Schema Import Feature permits the query Prolog to contain a ·schema import·.
If an XQuery implementation does not support the Schema Import Feature, it ·MUST· raise a static error [err:XPST0009]. if it encounters a schema import.
[Definition:] The
Schema Validation Feature permits a query to contain a
validate expression (see 3.13 Validate Expressions.)
If an XQuery implementation does not support the Schema Validation Feature, it
·MUST· raise a static error
[err:XPST0075].
if it encounters a validate expression.
[Definition:] The Static Typing Feature provides support for the static semantics defined in [XQuery 1.0 and XPath 2.0 Formal Semantics], and requires implementations to detect and report ·type errors· during the ·static analysis phase·.
If an implementation does not support the ·Static Typing Feature·, but can nevertheless determine during the static analysis phase that an expression, if evaluated, will necessarily raise a type error at run time, the implementation ·MAY· raise that error during the static analysis phase. The choice of whether to raise such an error at analysis time is ·implementation dependent·.
In some cases, the static typing rules defined in [XQuery 1.0 and XPath 2.0 Formal Semantics] are not very precise (see, for example, the
type inference rules for the ancestor axes—parent, ancestor, and
ancestor-or-self—and for the function fn:root). Some
implementations may wish to support more precise static typing rules.
A conforming implementation that implements the ·Static Typing Feature··MAY· also provide one or more static typing extensions. [Definition:] A static typing extension is an ·implementation-defined· type inference rule that infers a more precise static type than that inferred by the type inference rules in [XQuery 1.0 and XPath 2.0 Formal Semantics]. See for a formal definition of the constraints on static typing extensions.
[Definition:] The following axes are
designated as optional axes: ancestor,
ancestor-or-self, following,
following-sibling, preceding, and
preceding-sibling.
[Definition:] A conforming XQuery implementation that supports the Full Axis Feature·MUST· support all the ·optional axes·.
Conforming XQuery implementations that do not support the Full Axis Feature ·MAY· support one or more optional axes; it is ·implementation-defined· which optional axes are supported by such implementations. A conforming implementation that encounters a reference to an optional axis that it does not support ·MUST· raise a ·static error· [err:XPST0010]. .
namespace axis (defined by XPath 1.0
and deprecated by XPath 2.0).[Definition:] A conforming XQuery implementation that supports the Module Feature allows a query Prolog to contain a Module Import and allows library modules to be created.
A conforming implementation that does not support the Module Feature ·MUST· raise a ·static error· [err:XPST0016]. if it encounters a ·module declaration· or a ·module import·. Since a ·module declaration· is required in a ·library module·, the Module Feature is required in order to create a ·library module·.
[Definition:] A conforming XQuery implementation that supports the Serialization Feature·MUST· provide means for serializing the result of a query, as specified in 2.2.4 Serialization.
A conforming XQuery implementation that supports the Serialization Feature ·MUST· conform to C.3 Serialization Parameters. The means by which serialization is invoked is ·implementation-defined·.
If an error is raised during the serialization process as specified in [XSLT 2.0 and XQuery 1.0 Serialization], an conforming XQuery implementation ·MUST· report the error to the calling environment.
[Definition:] A conforming XQuery implementation that supports the Trivial XML Embedding Feature·MUST· provide the embedding specified in [XQueryX 1.0] Section 5, "A Trivial Embedding of XQuery."
5.3 Data Model ConformanceAll XQuery implementations process data represented in the ·data model· as specified in [XQuery/XPath Data Model (XDM)]. The data model specification relies on languages such as XQuery to specify conformance criteria for the data model in their respective environments, and suggests that the following issues should be considered:
xs:NCName and xs:ID are constrained by the XML 1.0 rules. It is recommended that an XQuery 1.0 processor should implement the rules defined by later versions of XML Schema as they become available.xs:decimal type, the maximum number of decimal digits
(totalDigits facet) (must be at least 18).xs:date, xs:time, xs:dateTime, xs:gYear,
and xs:gYearMonth: the maximum value of the year component and the maximum number of fractional second digits (must be at least 3).xs:duration type: the maximum absolute values of the
years, months, days, hours, minutes, and seconds components.xdt:yearMonthDuration type: the maximum absolute value,
expressed as an integer number of months.xdt:dayTimeDuration type: the maximum absolute value,
expressed as a decimal number of seconds.xs:string, xs:hexBinary, xs:base64Binary, xs:QName,
xs:anyURI, xs:NOTATION, and types derived from them: limitations (if any)
imposed by the implementation on lengths of values.xs:string may be limited by available memory.A.1 EBNFThe grammar of XQuery uses the same simple Extended Backus-Naur Form (EBNF) notation as [XML 1.0] with the following minor differences.
The terminal symbols for this grammar include the quoted strings used in the production rules below, and the terminal symbols defined in section A.2.1 Terminal Symbols.
The EBNF notation is described in more detail in A.1.1 Notation.
To increase readability, the EBNF in the main body of this document omits some of these notational features. This appendix is the normative version of the EBNF.
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The following definitions will be helpful in defining precisely this exposition.
[Definition:] Each rule in the grammar defines one symbol, using the following format:symbol ::= expression
[Definition:] A terminal is a symbol or string or pattern that can appear in the right-hand side of a rule, but never appears on the left hand side in the main grammar, although it may appear on the left-hand side of a rule in the grammar for terminals. The following constructs are used to match strings of one or more characters in a terminal:
Patterns (including the above constructs) can be combined with grammatical operators to form more complex patterns, matching more complex sets of character strings. In the examples that follow, A and B represent (sub-)patterns.
A is treated as a unit and may be combined as described in this list.A or nothing; optional A.A followed by B. This operator has higher precedence than alternation; thus A B | C D is identical to (A B) | (C D).A or B but not both.A but does not match B.A. Concatenation has higher precedence than alternation; thus A+ | B+ is identical to (A+) | (B+).A. Concatenation has higher precedence than alternation; thus A* | B* is identical to (A*) | (B*)This section contains constraints on the EBNF productions, which are required to parse legal sentences. The notes below are referenced from the right side of the production, with the notation: /* xgc: <id> */.
(/) * 5. The expression 5 *
/, on the other hand, is legal without parentheses.prefix : localname is not a valid QName for purposes
of this specification, just as it is not permitted in a XML document.
Also, comments are not permissible on either side of the colon. Also extra-grammatical constraints such as well-formedness constraints must be taken into account.if(foo) could be taken either as a FunctionCall or
as the beginning of an IfExpr. Therefore it is not legal
syntax for a user to invoke functions with unprefixed names
which match any of the names in A.3 Reserved Function Names.A function named "if" can be called by binding its namespace
to a prefix and using the prefixed form: "library:if(foo)"
instead of "if(foo)".4 treat as
item() + - 5 must be interpreted as (4 treat as item()+) - 5,
taking the '+' as an OccurrenceIndicator and the
'-' as a subtraction operator. To force the interpretation
of "+" as an addition operator (and the corresponding
interpretation of the "-" as a unary minus), parentheses
may be used: the form (4 treat as item()) + -5 surrounds
the SequenceType expression with parentheses and leads
to the desired interpretation.This rule has as a consequence that certain forms which
would otherwise be legal and unambiguous are not
recognized: in "4 treat as item() + 5", the "+" is
taken as an OccurrenceIndicator, and not as an operator,
which means this is not a legal expression.This section contains general notes on the EBNF productions, which may be helpful in understanding how to interpret and implement the EBNF. These notes are not normative. The notes below are referenced from the right side of the production, with the notation: /* gn: <id> */.
address (: this may be empty :) may be mistaken for a call to a function named "address" unless this lookahead is employed. Another example is for (: whom the bell :) $tolls in 3 return $tolls, where the keyword "for" must not be mistaken for a function name.(: commenting out a (: comment :) may be confusing, but often helpful :) is a legal Comment, since balanced nesting of comments is allowed."this is just a string :)" is a legal expression. However, (: "this is just a string :)" :) will cause a syntax error. Likewise, "this is another string (:" is a legal expression, but (: "this is another string (:" :) will cause a syntax error. It is a limitation of nested comments that literal content can cause unbalanced nesting of comments.for (: set up loop :) $i in $x return $i is syntactically legal, ignoring the comment.5 instance (: strange place for a comment :) of xs:integer is also syntactically legal.<eg (: an example:)>{$i//title}</eg> is not syntactically legal.<eg> (: an example:) </eg> is syntactically legal, but the characters that look like a comment are in
fact literal element content. A.2 Lexical structureThe terminal symbols assumed by the grammar above are described in this section.
Quoted strings appearing in production rules are terminal symbols.
Other terminal symbols are defined in A.2.1 Terminal Symbols.
It is ·implementation-defined· whether the lexical rules of [XML 1.0] and [XML Names] are followed, or alternatively, the lexical rules of [XML 1.1] and [XML Names 1.1] are followed. Implementations that support the full [XML 1.1] character set ·SHOULD·, for purposes of interoperability, provide a mode that follows only the [XML 1.0] and [XML Names] lexical rules.
When tokenizing, the longest possible match that is valid in the current context is used.
All keywords are case sensitive. Keywords are not reserved—that is, any QName may duplicate a keyword except as noted in A.3 Reserved Function Names.
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The following symbols are used only in the definition of terminal symbols; they are not terminal symbols in the grammar of A.1 EBNF.
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XQuery 1.0 expressions consist of terminal symbols and ·symbol separators·.
Terminal symbols are of two kinds: delimiting and non-delimiting.
[Definition:] The delimiting terminal symbols are: "=", ";", ",", "$", ":=", "(", ")", "!=", "<=", ">", ">=", "<<", ">>", "::", "@", "..", "*", "[", "]", ".", "?", "-", "+", PredefinedEntityRef, "{", "}", "{{", "}}", "<", """, "'", "/>", "</", "(#", "#)", "<?", "?>", "<![CDATA[", "]]>", "<!--", "-->", Comment, "/", "//", CharRef, ":", S
[Definition:] The non-delimiting terminal symbols are: "xquery", "version", "encoding", "module", "namespace", "declare", "boundary-space", "preserve", "strip", "default", "element", "function", "option", "ordering", "ordered", "unordered", "order", "empty", "copy-namespaces", "no-preserve", "inherit", "no-inherit", "collation", "base-uri", "import", "schema", "at", "variable", "construction", "as", "return", "for", "in", "let", "where", "by", "stable", "some", "every", "satisfies", "typeswitch", "case", "if", "then", "else", "eq", "ne", "lt", "le", "gt", "ge", "is", "validate", "lax", "strict", "child", "descendant", "attribute", "self", "descendant-or-self", "following-sibling", "following", "parent", "ancestor", "preceding-sibling", "preceding", "ancestor-or-self", "document", "text", "comment", "processing-instruction", "empty-sequence", "item", "node", "document-node", "schema-attribute", "schema-element", IntegerLiteral, DecimalLiteral, DoubleLiteral, StringLiteral, "external", "ascending", "descending", "greatest", "least", EscapeQuot, EscapeApos, ElementContentChar, QuotAttrContentChar, AposAttrContentChar, PITarget, QName, NCName, Char, Digits
[Definition:] ·Whitespace· and Comments function as symbol separators. For the most part, they are not mentioned in the grammar, and may occur between any two terminal symbols mentioned in the grammar, except where that is forbidden by the /* ws: explicit */ annotation in the EBNF, or by the /* xgs: xml-version */ annotation.
It is customary to separate consecutive terminal symbols by ·whitespace· and Comments, but this is required only when otherwise two non-delimiting symbols would be adjacent to each other. There are two exceptions to this, that of "." and "-", which do require a ·symbol separator· if they follow a QName or NCName.
The XQuery processor must behave as if it normalized all line breaks on input, before parsing. The normalization should be done according to the choice to support either [XML 1.0] or [XML 1.1] lexical processing.
For [XML 1.0] processing, all of the following must be translated to a single #xA character:
For [XML 1.1] processing, all of the following must be translated to a single #xA character:
The characters #x85 and #x2028 cannot be reliably recognized and translated until the VersionDecl declaration (if present) has been read.
[Definition:] A whitespace character is any of the characters defined by [http://www.w3.org/TR/REC-xml#NT-S].
[Definition:] Ignorable whitespace consists of any ·whitespace· characters that may occur between ·terminals·, unless these characters occur in the context of a production marked with a ws:explicit annotation, in which case they can occur only where explicitly specified (see A.2.4.2 Explicit Whitespace Handling). Ignorable whitespace characters are not significant to the semantics of an expression. Whitespace is allowed before the first terminal and after the last terminal of a module. Whitespace is allowed between any two ·terminals·. Comments may also act as "whitespace" to prevent two adjacent terminals from being recognized as one. Some illustrative examples are as follows:
foo- foo results in a syntax error. "foo-" would be recognized as a QName.foo -foo is syntactically equivalent to foo - foo, two QNames separated by a subtraction operator. foo(: This is a comment :)- foo is syntactically equivalent to foo - foo. This is because the comment prevents the two adjacent terminals from being recognized as one.foo-foo is syntactically equivalent to single QName. This is because "-" is a valid character in a QName.
When used as an operator after the characters of a name, the "-"
must be separated from the name, e.g. by using whitespace or
parentheses.10div 3 results in a syntax error.10 div3 also results in a syntax error.10div3 also results in a syntax error.Explicit whitespace notation is specified with the EBNF productions, when it is different from the default rules, using the notation shown below. This notation is not inherited. In other words, if an EBNF rule is marked as /* ws: explicit */, the notation does not automatically apply to all the 'child' EBNF productions of that rule.
S or otherwise, where ·whitespace characters· are allowed. In productions with the /* ws: explicit */ annotation, A.2.4.1 Default Whitespace Handling does not apply. Comments are also not allowed in these productions.For example, whitespace is not freely allowed by the direct constructor productions, but is specified explicitly in the grammar, in order to be more consistent with XML.
A.3 Reserved Function NamesThe following names are not allowed as function names in an unprefixed form because expression syntax takes precedence.
attributecommentdocument-nodeelementempty-sequenceifitemnodeprocessing-instructionschema-attributeschema-elementtexttypeswitch A.4 Precedence OrderThe grammar in A.1 EBNF normatively defines built-in precedence among the operators of XQuery. These operators are summarized here to make clear the order of their precedence from lowest to highest. Operators that have a lower precedence number cannot be contained by operators with a higher precedence number. The associativity column indicates the order in which operators of equal precedence in an expression are applied.
| # | Operator | Associativity |
|---|---|---|
| 1 | , (comma) | left-to-right |
| 2 | := (assignment) | right-to-left |
| 3 | for, some, every, typeswitch, if | left-to-right |
| 4 | or | left-to-right |
| 5 | and | left-to-right |
| 6 | eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, <<, >> | left-to-right |
| 7 | to | left-to-right |
| 8 | +, - | left-to-right |
| 9 | *, div, idiv, mod | left-to-right |
| 10 | union, | | left-to-right |
| 11 | intersect, except | left-to-right |
| 12 | instance of | left-to-right |
| 13 | treat | left-to-right |
| 14 | castable | left-to-right |
| 15 | cast | left-to-right |
| 16 | -(unary), +(unary) | right-to-left |
| 17 | ?, *(OccurrenceIndicator), +(OccurrenceIndicator) | left-to-right |
| 18 | /, // | left-to-right |
| 19 | [ ], ( ), {} | left-to-right |
B.1 Type Promotion[Definition:] Under certain circumstances, an atomic value can be promoted from
one type to another. Type promotion is used in evaluating function calls (see 3.1.5 Function Calls), order by clauses (see 3.8.3 Order By and Return Clauses), and operators that accept numeric or string operands (see B.2 Operator Mapping). The following type promotions are permitted:
xs:float (or any type
derived by restriction from xs:float) can be promoted to
the type xs:double. The result is the
xs:double value that is the same as the original
value.xs:decimal (or any type derived
by restriction from xs:decimal) can be promoted to either
of the types xs:float or xs:double. The
result of this promotion is created by casting the original value to
the required type. This kind of promotion may cause loss of
precision.xs:anyURI (or any type derived by restriction from xs:anyURI) can be promoted to the type xs:string. The result of this promotion is created by casting the original value to the type xs:string.xs:anyURI values can be promoted to xs:string, functions and operators that compare strings using the ·default collation· also compare xs:anyURI values using the ·default collation·. This ensures that orderings that include strings, xs:anyURI values, or any combination of the two types are consistent and well-defined.Note that ·type promotion· is different from ·subtype substitution·. For example:
$p of type xs:float can be invoked with a value of type xs:decimal. This is an example of ·type promotion·. The value is actually converted to the expected type. Within the body of the function, $p instance of xs:decimal returns false.$p of type xs:decimal can be invoked with a value of type xs:integer. This is an example of ·subtype substitution·. The value retains its original type. Within the body of the function, $p instance of xs:integer returns true. B.2 Operator MappingThe operator mapping tables in this section list the combinations of types for which the various operators of XQuery are defined. [Definition:] For each operator and valid combination of operand types, the operator mapping tables specify a result type and an operator function that implements the semantics of the operator for the given types. The definitions of the operator functions are given in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The result of an operator may be the raising of an error by its operator function, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In some cases, the operator function does not implement the full semantics of a given operator. For the definition of each operator (including its behavior for empty sequences or sequences of length greater than one), see the descriptive material in the main part of this document.
The and and
or operators are defined directly in the main body of
this document, and do not occur in the operator mapping tables.
Any operator listed in the operator mapping tables may be validly
applied to an operand of type AT if the table calls for
an operand of type ET and
type-matches(ET, AT) is
true (see 2.5.4 SequenceType Matching). For
example, a table entry indicates that the gt operator may
be applied to two xs:date operands, returning
xs:boolean. Therefore, the gt operator may
also be applied to two (possibly different) subtypes of
xs:date, also returning xs:boolean.
[Definition:] When referring to a type, the term numeric denotes the types
xs:integer, xs:decimal,
xs:float, and xs:double. An operator whose
operands and result are designated as ·numeric· might be
thought of as representing four operators, one for each of the numeric
types. For example, the numeric + operator might be
thought of as representing the following four operators:
| Operator | First operand type | Second operand type | Result type |
+ | xs:integer | xs:integer | xs:integer |
+ | xs:decimal | xs:decimal | xs:decimal |
+ | xs:float | xs:float | xs:float |
+ | xs:double | xs:double | xs:double |
A numeric operator may be validly applied to an operand of type AT if type-matches(ET, AT) is true where ET is any of the four numeric types. If the result type of an operator is listed as numeric, it means "the first type in the ordered list (xs:integer, xs:decimal, xs:float, xs:double) into which all operands can be converted by ·subtype substitution· and ·type promotion·." As an example, suppose that the type hatsize is derived from xs:integer and the type shoesize is derived from xs:float. Then if the + operator is invoked with operands of type hatsize and shoesize, it returns a result of type xs:float. Similarly, if + is invoked with two operands of type hatsize it returns a result of type xs:integer.
[Definition:] In the operator mapping tables,
the term Gregorian refers to the types
xs:gYearMonth, xs:gYear,
xs:gMonthDay, xs:gDay, and
xs:gMonth. For binary operators that accept two
Gregorian-type operands, both operands must have the same type (for
example, if one operand is of type xs:gDay, the other
operand must be of type xs:gDay.)
| Operator | Type(A) | Type(B) | Function | Result type |
|---|---|---|---|---|
| A + B | numeric | numeric | op:numeric-add(A, B) | numeric |
| A + B | xs:date | xdt:yearMonthDuration | op:add-yearMonthDuration-to-date(A, B) | xs:date |
| A + B | xdt:yearMonthDuration | xs:date | op:add-yearMonthDuration-to-date(B, A) | xs:date |
| A + B | xs:date | xdt:dayTimeDuration | op:add-dayTimeDuration-to-date(A, B) | xs:date |
| A + B | xdt:dayTimeDuration | xs:date | op:add-dayTimeDuration-to-date(B, A) | xs:date |
| A + B | xs:time | xdt:dayTimeDuration | op:add-dayTimeDuration-to-time(A, B) | xs:time |
| A + B | xdt:dayTimeDuration | xs:time | op:add-dayTimeDuration-to-time(B, A) | xs:time |
| A + B | xs:dateTime | xdt:yearMonthDuration | op:add-yearMonthDuration-to-dateTime(A, B) | xs:dateTime |
| A + B | xdt:yearMonthDuration | xs:dateTime | op:add-yearMonthDuration-to-dateTime(B, A) | xs:dateTime |
| A + B | xs:dateTime | xdt:dayTimeDuration | op:add-dayTimeDuration-to-dateTime(A, B) | xs:dateTime |
| A + B | xdt:dayTimeDuration | xs:dateTime | op:add-dayTimeDuration-to-dateTime(B, A) | xs:dateTime |
| A + B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:add-yearMonthDurations(A, B) | xdt:yearMonthDuration |
| A + B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:add-dayTimeDurations(A, B) | xdt:dayTimeDuration |
| A - B | numeric | numeric | op:numeric-subtract(A, B) | numeric |
| A - B | xs:date | xs:date | op:subtract-dates(A, B) | xdt:dayTimeDuration |
| A - B | xs:date | xdt:yearMonthDuration | op:subtract-yearMonthDuration-from-date(A, B) | xs:date |
| A - B | xs:date | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-date(A, B) | xs:date |
| A - B | xs:time | xs:time | op:subtract-times(A, B) | xdt:dayTimeDuration |
| A - B | xs:time | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-time(A, B) | xs:time |
| A - B | xs:dateTime | xs:dateTime | op:subtract-dateTimes(A, B) | xdt:dayTimeDuration |
| A - B | xs:dateTime | xdt:yearMonthDuration | op:subtract-yearMonthDuration-from-dateTime(A, B) | xs:dateTime |
| A - B | xs:dateTime | xdt:dayTimeDuration | op:subtract-dayTimeDuration-from-dateTime(A, B) | xs:dateTime |
| A - B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:subtract-yearMonthDurations(A, B) | xdt:yearMonthDuration |
| A - B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:subtract-dayTimeDurations(A, B) | xdt:dayTimeDuration |
| A * B | numeric | numeric | op:numeric-multiply(A, B) | numeric |
| A * B | xdt:yearMonthDuration | numeric | op:multiply-yearMonthDuration(A, B) | xdt:yearMonthDuration |
| A * B | numeric | xdt:yearMonthDuration | op:multiply-yearMonthDuration(B, A) | xdt:yearMonthDuration |
| A * B | xdt:dayTimeDuration | numeric | op:multiply-dayTimeDuration(A, B) | xdt:dayTimeDuration |
| A * B | numeric | xdt:dayTimeDuration | op:multiply-dayTimeDuration(B, A) | xdt:dayTimeDuration |
| A idiv B | numeric | numeric | op:numeric-integer-divide(A, B) | xs:integer |
| A div B | numeric | numeric | op:numeric-divide(A, B) | numeric; but xs:decimal if both operands are xs:integer |
| A div B | xdt:yearMonthDuration | numeric | op:divide-yearMonthDuration(A, B) | xdt:yearMonthDuration |
| A div B | xdt:dayTimeDuration | numeric | op:divide-dayTimeDuration(A, B) | xdt:dayTimeDuration |
| A div B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:divide-yearMonthDuration-by-yearMonthDuration (A, B) | xs:decimal |
| A div B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:divide-dayTimeDuration-by-dayTimeDuration (A, B) | xs:decimal |
| A mod B | numeric | numeric | op:numeric-mod(A, B) | numeric |
| A eq B | numeric | numeric | op:numeric-equal(A, B) | xs:boolean |
| A eq B | xs:boolean | xs:boolean | op:boolean-equal(A, B) | xs:boolean |
| A eq B | xs:string | xs:string | op:numeric-equal(fn:compare(A, B), 0) | xs:boolean |
| A eq B | xs:date | xs:date | op:date-equal(A, B) | xs:boolean |
| A eq B | xs:time | xs:time | op:time-equal(A, B) | xs:boolean |
| A eq B | xs:dateTime | xs:dateTime | op:datetime-equal(A, B) | xs:boolean |
| A eq B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-equal(A, B) | xs:boolean |
| A eq B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-equal(A, B) | xs:boolean |
| A eq B | xs:duration | xs:duration | op:duration-equal(A, B) | xs:boolean |
| A eq B | Gregorian | Gregorian | op:gYear-equal(A, B) etc. | xs:boolean |
| A eq B | xs:hexBinary | xs:hexBinary | op:hex-binary-equal(A, B) | xs:boolean |
| A eq B | xs:base64Binary | xs:base64Binary | op:base64-binary-equal(A, B) | xs:boolean |
| A eq B | xs:anyURI | xs:anyURI | op:numeric-equal(fn:compare(A, B), 0) | xs:boolean |
| A eq B | xs:QName | xs:QName | op:QName-equal(A, B) | xs:boolean |
| A eq B | xs:NOTATION | xs:NOTATION | op:NOTATION-equal(A, B) | xs:boolean |
| A ne B | numeric | numeric | fn:not(op:numeric-equal(A, B)) | xs:boolean |
| A ne B | xs:boolean | xs:boolean | fn:not(op:boolean-equal(A, B)) | xs:boolean |
| A ne B | xs:string | xs:string | fn:not(op:numeric-equal(fn:compare(A, B), 0)) | xs:boolean |
| A ne B | xs:date | xs:date | fn:not(op:date-equal(A, B)) | xs:boolean |
| A ne B | xs:time | xs:time | fn:not(op:time-equal(A, B)) | xs:boolean |
| A ne B | xs:dateTime | xs:dateTime | fn:not(op:datetime-equal(A, B)) | xs:boolean |
| A ne B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-equal(A, B)) | xs:boolean |
| A ne B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-equal(A, B) | xs:boolean |
| A ne B | xs:duration | xs:duration | fn:not(op:duration-equal(A, B)) | xs:boolean |
| A ne B | Gregorian | Gregorian | fn:not(op:gYear-equal(A, B)) etc. | xs:boolean |
| A ne B | xs:hexBinary | xs:hexBinary | fn:not(op:hex-binary-equal(A, B)) | xs:boolean |
| A ne B | xs:base64Binary | xs:base64Binary | fn:not(op:base64-binary-equal(A, B)) | xs:boolean |
| A ne B | xs:anyURI | xs:anyURI | fn:not(op:numeric-equal(fn:compare(A, B), 0)) | xs:boolean |
| A ne B | xs:QName | xs:QName | fn:not(op:QName-equal(A, B)) | xs:boolean |
| A ne B | xs:NOTATION | xs:NOTATION | fn:not(op:NOTATION-equal(A, B)) | xs:boolean |
| A gt B | numeric | numeric | op:numeric-greater-than(A, B) | xs:boolean |
| A gt B | xs:boolean | xs:boolean | op:boolean-greater-than(A, B) | xs:boolean |
| A gt B | xs:string | xs:string | op:numeric-greater-than(fn:compare(A, B), 0) | xs:boolean |
| A gt B | xs:date | xs:date | op:date-greater-than(A, B) | xs:boolean |
| A gt B | xs:time | xs:time | op:time-greater-than(A, B) | xs:boolean |
| A gt B | xs:dateTime | xs:dateTime | op:datetime-greater-than(A, B) | xs:boolean |
| A gt B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-greater-than(A, B) | xs:boolean |
| A gt B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-greater-than(A, B) | xs:boolean |
| A lt B | numeric | numeric | op:numeric-less-than(A, B) | xs:boolean |
| A lt B | xs:boolean | xs:boolean | op:boolean-less-than(A, B) | xs:boolean |
| A lt B | xs:string | xs:string | op:numeric-less-than(fn:compare(A, B), 0) | xs:boolean |
| A lt B | xs:date | xs:date | op:date-less-than(A, B) | xs:boolean |
| A lt B | xs:time | xs:time | op:time-less-than(A, B) | xs:boolean |
| A lt B | xs:dateTime | xs:dateTime | op:datetime-less-than(A, B) | xs:boolean |
| A lt B | xdt:yearMonthDuration | xdt:yearMonthDuration | op:yearMonthDuration-less-than(A, B) | xs:boolean |
| A lt B | xdt:dayTimeDuration | xdt:dayTimeDuration | op:dayTimeDuration-less-than(A, B) | xs:boolean |
| A ge B | numeric | numeric | op:numeric-greater-than(A, B) or op:numeric-equal(A, B) | xs:boolean |
| A ge B | xs:boolean | xs:boolean | fn:not(op:boolean-less-than(A, B)) | xs:boolean |
| A ge B | xs:string | xs:string | op:numeric-greater-than(fn:compare(A, B), -1) | xs:boolean |
| A ge B | xs:date | xs:date | fn:not(op:date-less-than(A, B)) | xs:boolean |
| A ge B | xs:time | xs:time | fn:not(op:time-less-than(A, B)) | xs:boolean |
| A ge B | xs:dateTime | xs:dateTime | fn:not(op:datetime-less-than(A, B)) | xs:boolean |
| A ge B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-less-than(A, B)) | xs:boolean |
| A ge B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-less-than(A, B)) | xs:boolean |
| A le B | numeric | numeric | op:numeric-less-than(A, B) or op:numeric-equal(A, B) | xs:boolean |
| A le B | xs:boolean | xs:boolean | fn:not(op:boolean-greater-than(A, B)) | xs:boolean |
| A le B | xs:string | xs:string | op:numeric-less-than(fn:compare(A, B), 1) | xs:boolean |
| A le B | xs:date | xs:date | fn:not(op:date-greater-than(A, B)) | xs:boolean |
| A le B | xs:time | xs:time | fn:not(op:time-greater-than(A, B)) | xs:boolean |
| A le B | xs:dateTime | xs:dateTime | fn:not(op:datetime-greater-than(A, B)) | xs:boolean |
| A le B | xdt:yearMonthDuration | xdt:yearMonthDuration | fn:not(op:yearMonthDuration-greater-than(A, B)) | xs:boolean |
| A le B | xdt:dayTimeDuration | xdt:dayTimeDuration | fn:not(op:dayTimeDuration-greater-than(A, B)) | xs:boolean |
| A is B | node() | node() | op:is-same-node(A, B) | xs:boolean |
| A << B | node() | node() | op:node-before(A, B) | xs:boolean |
| A >> B | node() | node() | op:node-after(A, B) | xs:boolean |
| A union B | node()* | node()* | op:union(A, B) | node()* |
| A | B | node()* | node()* | op:union(A, B) | node()* |
| A intersect B | node()* | node()* | op:intersect(A, B) | node()* |
| A except B | node()* | node()* | op:except(A, B) | node()* |
| A to B | xs:integer | xs:integer | op:to(A, B) | xs:integer* |
| A , B | item()* | item()* | op:concatenate(A, B) | item()* |
| Operator | Operand type | Function | Result type |
|---|---|---|---|
| + A | numeric | op:numeric-unary-plus(A) | numeric |
| - A | numeric | op:numeric-unary-minus(A) | numeric |
The tables in this section describe how values are assigned to the various components of the static context and dynamic context, and to the parameters that control the serialization process.
C.1 Static Context ComponentsThe following table describes the components of the static context. The following aspects of each component are described:
| Component | Default initial value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
|---|---|---|---|---|---|
| XPath 1.0 Compatibility Mode | false | no | no | global | Must be false. |
| Statically known namespaces | fn, xml, xs, xsi, xdt, local | overwriteable and augmentable (except for xml) | overwriteable and augmentable by prolog or element constructor | lexical | Only one namespace can be assigned to a given prefix per lexical scope. |
| Default element/type namespace | no namespace | overwriteable | overwriteable by prolog or element constructor | lexical | Only one default namespace per lexical scope. |
| Default function namespace | fn | overwriteable (not recommended) | overwriteable by prolog | module | None. |
| In-scope schema types | built-in types in xs, xdt | augmentable | augmentable by schema import in prolog | module | Only one definition per global or local type. |
| In-scope element declarations | none | augmentable | augmentable by schema import in prolog | module | Only one definition per global or local element name. |
| In-scope attribute declarations | none | augmentable | augmentable by schema import in prolog | module | Only one definition per global or local attribute name. |
| In-scope variables | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | lexical | Only one definition per variable per lexical scope. |
| Context item static type | none (raises error on access) | overwriteable | not explicitly, but can be influenced by expressions | lexical | None. |
| Function signatures | functions in fn namespace, and constructors for built-in atomic types | augmentable | augmentable by module import and by function declaration in prolog | module | Each function must have a unique expanded QName and number of arguments. |
| Statically known collations | only the default collation | augmentable | no | module | Each URI uniquely identifies a collation. |
| Default collation | Unicode codepoint collation | overwriteable | overwriteable by prolog | module | None. |
| Construction mode | preserve | overwriteable | overwriteable by prolog | module | Value must be preserve or strip. |
| Ordering mode | ordered | overwriteable | overwriteable by prolog or expression | lexical | Value must be ordered or unordered. |
| Default order for empty sequences | implementation-defined | overwriteable | overwriteable by prolog | module | Value must be greatest or least. |
| Boundary-space policy | strip | overwriteable | overwriteable by prolog | module | Value must be preserve or strip. |
| Copy-namespaces mode | inherit, preserve | overwriteable | overwriteable by prolog | module | Value consists of inherit or no-inherit, and preserve or no-preserve. |
| Base URI | none | overwriteable | overwriteable by prolog | module | Value must be a valid lexical representation of the type xs:anyURI. |
| Statically known documents | none | augmentable | no | module | None. |
| Statically known collections | none | augmentable | no | module | None. |
| Statically known default collection type | node()* | overwriteable | no | module | None. |
C.2 Dynamic Context ComponentsThe following table describes the components of the dynamic context. The following aspects of each component are described:
| Component | Default initial value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
|---|---|---|---|---|---|
| Context item | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | None |
| Context position | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | If context item is defined, context position must be >0 and <= context size; else context position is undefined. |
| Context size | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | If context item is defined, context size must be >0; else context size is undefined. |
| Variable values | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | dynamic | Names and values must be consistent with in-scope variables. |
| Function implementations | functions in fn namespace, and constructors for built-in atomic types | augmentable | augmentable by module import and by function declaration in prolog | global | Must be consistent with function signatures |
| Current dateTime | none | must be initialized by implementation | no | global | Must include a timezone. Remains constant during evaluation of a query. |
| Implicit timezone | none | must be initialized by implementation | no | global | Remains constant during evaluation of a query. |
| Available documents | none | must be initialized by implementation | no | global | None |
| Available collections | none | must be initialized by implementation | no | global | None |
| Default collection | none | overwriteable | no | global | None |
C.3 Serialization ParametersThe following table specifies default values for the parameters that control the process of serializing an ·XDM instance· into XML notation (method = "xml"). The meanings of the various parameters are defined in [XSLT 2.0 and XQuery 1.0 Serialization]. For each parameter, an XQuery implementation may (but is not required to) provide a means whereby a user can override the default value.
| Parameter | Default Value |
|---|---|
| byte-order-mark | implementation-defined |
| cdata-section-elements | empty |
| doctype-public | (none) |
| doctype-system | (none) |
| encoding | implementation-defined choice between "utf-8" and "utf-16" |
| escape-uri-attributes | (not applicable when method = xml) |
| include-content-type | (not applicable when method = xml) |
| indent | no |
| media-type | implementation-defined |
| method | xml |
| normalization-form | implementation-defined |
| omit-xml-declaration | implementation-defined |
| standalone | implementation-defined |
| undeclare-prefixes | no |
| use-character-maps | empty |
| version | implementation-defined |
The following items in this specification are ·implementation-defined·:
order by clause (empty least or empty greatest).byte-order-mark, encoding, media-type, normalization-form, omit-xml-declaration, standalone, and version parameters, if the ·Serialization Feature· is supported.E.1 Normative References E.2 Non-normative References E.3 Background MaterialIt is a ·static error· if analysis of an expression relies on some component of the ·static context· that has not been assigned a value.
It is a ·dynamic error· if evaluation of an expression relies on some part of the ·dynamic context· that has not been assigned a value.
It is a ·static error· if an expression is not a valid instance of the grammar defined in A.1 EBNF.
It is a ·type error· if, during the ·static analysis phase·, an expression is found to have a ·static type· that is not appropriate for the context in which the expression occurs, or during the ·dynamic evaluation phase·, the ·dynamic type· of a value does not match a required type as specified by the matching rules in 2.5.4 SequenceType Matching.
During the analysis phase,
it is a ·static error·
if the ·static type· assigned to an
expression other than the expression () or data(()) is empty-sequence().
(Not currently used.)
(Not currently used.)
It is a ·static error· if an expression refers to an element name, attribute name, schema type name, namespace prefix, or variable name that is not defined in the ·static context·, except within an ElementTest or an AttributeTest.
An implementation that does not support the Schema Import Feature must raise a ·static error· if a Prolog contains a schema import.
An implementation must raise a ·static error· if it encounters a reference to an axis that it does not support.
It is a ·static error· if the set of definitions contained in all schemas imported by a Prolog do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema] Part 1--i.e., each definition must be valid, complete, and unique.
It is a ·static error· if an implementation recognizes a pragma but determines that its content is invalid.
(Not currently used.)
(Not currently used.)
An implementation that does not support the Module Feature raises a ·static error· if it encounters a ·module declaration· or a ·module import·.
It is a ·static error· if the expanded QName and number of arguments in a function call do not match the name and arity of a ·function signature· in the ·static context·.
It is a ·type error· if the result of the last step in a path expression contains both nodes and atomic values.
It is a ·type error· if the result of a step (other than the last step) in a path expression contains an atomic value.
It is a ·type error· if, in an axis step, the context item is not a node.
(Not currently used.)
It is a ·static error· if the value of a ·namespace declaration attribute· is not a URILiteral.
(Not currently used.)
It is a ·type error· if the content sequence in an element constructor contains an attribute node following a node that is not an attribute node.
It is a ·dynamic error· if any attribute of a constructed element does not have a name that is distinct from the names of all other attributes of the constructed element.
It is a ·dynamic
error· if the result of the content expression of a computed processing instruction constructor contains the string "?>".
In a validate expression,
it is a ·dynamic error· if
the root element information item in the PSVI resulting from validation does not have the expected validity property: valid if validation mode is strict, or either valid or notKnown if validation mode is lax.
(Not currently used.)
(Not currently used.)
It is a ·type error·
if the argument of a validate expression does not
evaluate to exactly one document or element node.
It is a ·static error· if the version number specified in a version declaration is not supported by the implementation.
A ·static error· is raised if a Prolog contains more than one ·base URI declaration·.
It is a ·static error· if a Prolog contains multiple declarations for the same namespace prefix.
It is a ·static error· if multiple functions declared or imported by a ·module· have the same expanded QName and the same number of arguments.
It is a ·static error· to import two schema components that both define the same name in the same symbol space and in the same scope.
It is a ·static error· to import a module if the importing module's ·in-scope schema types· do not include definitions for the schema type names that appear in variable declarations, function parameters, or function returns found in the imported module.
(Not currently used.)
It is a ·static error· if a Prolog contains more than one ·default collation declaration·, or the value specified by a default collation declaration is not present in ·statically known collations·.
It is a ·static error· for a function declaration to have more than one parameter with the same name.
It is a ·static error· if the attributes specified by a direct element constructor do not have distinct expanded QNames.
It is a ·dynamic error·
if the value of the name expression in a computed processing instruction constructor cannot be cast to the type xs:NCName.
(Not currently used.)
(Not currently used.)
It is a ·dynamic error·
if the node-name property of the node constructed by a computed attribute constructor is in the namespace http://www.w3.org/2000/xmlns/ (corresponding to namespace prefix xmlns), or is in no namespace and has local name xmlns.
It is a ·static error·
if the function name in a function declaration is in one of the following namespaces: http://www.w3.org/XML/1998/namespace, http://www.w3.org/2001/XMLSchema, http://www.w3.org/2001/XMLSchema-instance, http://www.w3.org/2005/xpath-functions, http://www.w3.org/2005/xpath-datatypes.
An implementation ·MAY· raise a ·static error· if the value of a URILiteral is of nonzero length and is not in the lexical
space of xs:anyURI, or if it is a string that represents a "relative reference" as
defined in [RFC3986].
It is a ·static error· if multiple module imports in the same Prolog specify the same target namespace.
It is a ·static error· if a function or variable declared in a library module is not in the target namespace of the library module.
It is a ·static error· if more than one variable declared or imported by a ·module· has the same expanded QName.
It is a ·dynamic error·
if the ·dynamic type· of the operand of a treat expression does not match the ·sequence type· specified by the treat expression. This error might also be raised by a path expression beginning with "/" or "//" if the context node is not in a tree that is rooted at a document node. This is because a leading "/" or "//" in a path expression is an abbreviation for an initial step that includes the clause treat as document-node().
It is a ·static error· if a QName that is used as an AtomicType in a SequenceType is not defined in the ·in-scope schema types· as an atomic type.
(Not currently used.)
(Not currently used.)
It is a ·static error· if the ·initializing expression· in a variable declaration cannot be executed because of a circularity (for example, the expression depends on a function that in turn depends on the value of the initialized variable).
It is a ·static error· if a Prolog contains more than one ·copy-namespaces declaration·.
(Not currently used.)
It is a ·static error· if a schema import binds a namespace prefix but does not specify a target namespace other than a zero-length string.
It is a ·static error· if multiple schema imports specify the same target namespace.
It is a ·static error· if an implementation is unable to process a schema or module import by finding a schema or module with the specified target namespace.
It is a ·static error· if the name of a function in a function declaration is not in a namespace (expanded QName has a null namespace URI).
It is a ·dynamic error· if the operand of a validate expression is a document node whose children do not consist of exactly one element node and zero or more comment and processing instruction nodes, in any order.
(Not currently used.)
(Not currently used.)
It is a ·dynamic error· if the value of the name expression in a computed processing instruction constructor is equal to "XML" (in any combination of upper and lower case).
A ·static error· is raised if a Prolog contains more than one ·ordering mode declaration·.
A ·static error· is raised if a Prolog contains more than one default element/type namespace declaration, or more than one default function namespace declaration.
A ·static error· is raised if a Prolog contains more than one ·construction declaration·.
A ·static error· is raised if a Prolog contains more than one ·boundary-space declaration·.
A ·static error· is raised if a Prolog contains more than one ·empty order declaration·.
A ·static error· is raised
if the predefined namespace prefix xml or xmlns is redeclared by a namespace declaration or namespace declaration attribute, or if another namespace prefix is bound to the namespace URI associated with the prefix xml.
A ·static error· is raised if the namespace declaration attributes of a direct element constructor do not have distinct names.
It is a ·dynamic error· if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.
It is a ·static error· if the graph of ·module imports· contains a cycle (that is, if there exists a sequence of modules M1 ... Mn such that each Mi imports Mi+1 and Mn imports M1), unless all the modules in the cycle share a common namespace.
It is a ·dynamic error· if the value of the name expression in a computed element or attribute constructor cannot be converted to an ·expanded QName· (for example, because it contains a namespace prefix not found in ·statically known namespaces·.)
An implementation that does not support the Validation Feature must raise a ·static error· if
it encounters a validate expression.
It is a ·static
error·
if a collation subclause in an order by clause of a FLWOR expression does not identify a collation that is present in ·statically known collations·.
(Not currently used.)
(Not currently used.)
It is a ·static error· if an extension expression contains neither a ·pragma· that is recognized by the implementation nor an expression enclosed in curly braces.
The target type of a cast or castable expression must be an atomic type that is in the ·in-scope schema types· and is not xs:NOTATION or xdt:anyAtomicType, optionally followed by the occurrence indicator "?"; otherwise a ·static
error· is raised.
It is a ·static error· if a QName used in a query contains a namespace prefix that cannot be expanded into a namespace URI by using the ·statically known namespaces·.
(Not currently used.)
It is a ·static
error·
if the target type of a cast expression or constructor function is xs:QName or a type derived from xs:QName or xs:NOTATION, and the argument of the cast expression or constructor function is not a string literal.
It is a ·dynamic error·
if the element validated by a validate statement does not have a top-level element declaration in the ·in-scope element declarations·, if validation mode is strict.
It is a ·static error· if the namespace URI in a namespace declaration attribute is a zero-length string, and the implementation does not support [XML Names 1.1].
It is a ·type error·
if the typed value of a copied element or attribute node is ·namespace-sensitive· when ·construction mode· is preserve and ·copy-namespaces mode· is no-preserve.
It is a ·static
error·
if the encoding specified in a Version Declaration does not conform to the definition of EncName specified in [XML 1.0].
It is a ·static error· if the literal that specifies the target namespace in a ·module import· is of zero length.
application/xquery Media TypeThis Appendix specifies the media type for XQuery Version 1.0. XQuery is a language for querying over collections of data from XML data sources, as specified in the main body of this document. This media type is being submitted to the IESG (Internet Engineering Steering Group) for review, approval, and registration with IANA (Internet Assigned Numbers Authority.)
G.1 Introduction
This document, together with its normative references, defines the language XQuery Version 1.0. This Appendix
provides information about the application/xquery media type,
which is intended to be used for transmitting queries written in the
XQuery language.
This document was prepared by members of the W3C XML Query Working Group. Please send comments to public-qt-comments@w3.org, a public mailing list with archives at http://lists.w3.org/Archives/Public/public-qt-comments.
G.2 Registration of MIME Media Type application/xqueryMIME media type name: application
MIME subtype name: xquery
Required parameters: none
Optional parameters: none
The syntax of XQuery is expressed in Unicode but may be written
with any Unicode-compatible character encoding, including UTF-8 or
UTF-16, or transported as US-ASCII or Latin-1 with Unicode
characters outside the range of the given encoding represented using
an XML-style ෝ syntax.
The public XQuery Web page lists more than two dozen implementations of the XQuery language, both proprietary and open source.
This new media type is being registered to allow for deployment of XQuery on the World Wide Web.
G.3 Encoding ConsiderationsFor use with transports that are not 8-bit clean, quoted-printable encoding is recommended since the XQuery syntax itself uses the US-ASCII-compatible subset of Unicode.
An XQuery document may contain an ·encoding declaration· as part of its ·version declaration·:
xquery version "1.0" encoding "utf-8";
G.4 Recognizing XQuery FilesAn XQuery file may have the string xquery version "V.V" near the
beginning of the document, where "V.V" is a version number.
Currently the version number, if present, must be "1.0".
G.5 Charset Default RulesXQuery documents use the Unicode character set and, by default, the UTF-8 encoding.
G.6 Security ConsiderationsQueries written in XQuery may cause arbitrary URIs or IRIs to be
dereferenced. Therefore, the security issues of [RFC3987] Section 8 should be considered.
In addition, the contents of file: URIs can in some cases be
accessed, processed and returned as results.
Furthermore, because the XQuery language permits extensions,
it is possible that application/xquery
may describe content that has
security implications beyond those described here.
The XML Query Working group is working on a facility to allow XQuery expressions to be used to create and update persistent data. Untrusted queries should not be given write access to data.
This section contains examples of several important classes of queries that can be expressed using XQuery. The applications described here include joins across multiple data sources, grouping and aggregation, queries based on sequential relationships, recursive transformations, and selection of distinct combinations of values.
I.1 JoinsJoins, which combine data from multiple sources into a single result, are a very important type of query. In this section we will illustrate how several types of joins can be expressed in XQuery. We will base our examples on the following three documents:
parts.xml that
contains many
part elements;
each part
element in turn
contains
partno and
description
subelements.suppliers.xml that
contains many
supplier
elements; each
supplier
element in turn
contains
suppno and
suppname
subelements.catalog.xml that
contains information
about the
relationships between
suppliers and
parts. The catalog
document contains many
item elements,
each of which in turn
contains
partno,
suppno, and
price
subelements.A conventional ("inner") join returns information from two or more related sources, as illustrated by the following example, which combines information from three documents. The example generates a "descriptive catalog" derived from the catalog document, but containing part descriptions instead of part numbers and supplier names instead of supplier numbers. The new catalog is ordered alphabetically by part description and secondarily by supplier name.
<descriptive-catalog>
{
for $i in fn:doc("catalog.xml")/items/item,
$p in fn:doc("parts.xml")/parts/part[partno = $i/partno],
$s in fn:doc("suppliers.xml")/suppliers
/supplier[suppno = $i/suppno]
order by $p/description, $s/suppname
return
<item>
{
$p/description,
$s/suppname,
$i/price
}
</item>
}
</descriptive-catalog>The previous query returns information only about parts that have suppliers and suppliers that have parts. An outer join is a join that preserves information from one or more of the participating sources, including elements that have no matching element in the other source. For example, a left outer join between suppliers and parts might return information about suppliers that have no matching parts.
The following query demonstrates a left outer join. It returns names of all the suppliers in alphabetic order, including those that supply no parts. In the result, each supplier element contains the descriptions of all the parts it supplies, in alphabetic order.
for $s in fn:doc("suppliers.xml")/suppliers/supplier
order by $s/suppname
return
<supplier>
{
$s/suppname,
for $i in fn:doc("catalog.xml")/items/item
[suppno = $s/suppno],
$p in fn:doc("parts.xml")/parts/part
[partno = $i/pno]
order by $p/description
return $p/description
}
</supplier>The previous query preserves information about
suppliers that supply no parts. Another type of join,
called a full outer join, might be used
to preserve information about both suppliers that
supply no parts and parts that have no supplier. The
result of a full outer join can be structured in any
of several ways. The following query generates a list
of supplier elements, each containing
nested part elements for the parts that
it supplies (if any), followed by a list of
part elements for the parts that have no
supplier. This might be thought of as a
"supplier-centered" full outer join. Other forms of
outer join queries are also possible.
<master-list>
{
for $s in fn:doc("suppliers.xml")/suppliers/supplier
order by $s/suppname
return
<supplier>
{
$s/suppname,
for $i in fn:doc("catalog.xml")/items/item
[suppno = $s/suppno],
$p in fn:doc("parts.xml")/parts/part
[partno = $i/partno]
order by $p/description
return
<part>
{
$p/description,
$i/price
}
</part>
}
</supplier>
,
(: parts that have no supplier :)
<orphan-parts>
{ for $p in fn:doc("parts.xml")/parts/part
where fn:empty(fn:doc("catalog.xml")/items/item
[partno = $p/partno] )
order by $p/description
return $p/description
}
</orphan-parts>
}
</master-list>The previous query uses an element constructor to
enclose its output inside a master-list
element. The concatenation operator (",") is used to
combine the two main parts of the query. The result is
an ordered sequence of supplier elements
followed by an orphan-parts element that
contains descriptions of all the parts that have no
supplier.
I.2 GroupingMany queries
involve forming data into groups and
applying some aggregation function
such as fn:count or
fn:avg to each group. The
following example shows how such a
query might be expressed in XQuery,
using the catalog document defined in
the previous section.
This query finds the part number and average price for parts that have at least 3 suppliers.
for $pn in fn:distinct-values(
fn:doc("catalog.xml")/items/item/partno)
let $i := fn:doc("catalog.xml")/items/item[partno = $pn]
where fn:count($i) >= 3
order by $pn
return
<well-supplied-item>
<partno> {$p} </partno>
<avgprice> {fn:avg($i/price)} </avgprice>
</well-supplied-item>The fn:distinct-values function
in this query eliminates duplicate
part numbers from the set of all part
numbers in the catalog document. The
result of fn:distinct-values is a
sequence in which order is not
significant.
Note that $pn, bound by a
for clause, represents an individual
part number, whereas $i, bound by a
let clause, represents a set of items
which serves as argument to the
aggregate functions
fn:count($i) and
fn:avg($i/price). The query
uses an element constructor to enclose
each part number and average price in
a containing element called
well-supplied-item.
The method illustrated above generalizes easily to grouping by more than one data value. For example, consider a census document containing a sequence of person elements, each with subelements named state, job, and income. A census analyst might need to prepare a report listing the average income for each combination of state and job. This report might be produced using the following query:
for $s in fn:distinct-values(
fn:doc("census.xml")/census/person/state),
$j in fn:distinct-values(
fn:doc("census.xml")/census/person/job)
let $p := fn:doc("census.xml")/census/person
[state = $s and job = $j]
order by $s, $j
return
if (fn:exists($p)) then
<group>
<state> {$s} </state>
<job> {$j} </job>
<avgincome> {fn:avg($p/income)} </avgincome>
</group>
else ()The if-then-else expression in the above example prevents generation of groups that contain no data. For example, the census data may contain some persons who live in Nebraska, and some persons whose job is Deep Sea Fisherman, but no persons who live in Nebraska and have the job of Deep Sea Fisherman. If output groups are desired for all possible combinations of states and jobs, the if-then-else expression can be omitted from the query. In this case, the output may include "empty" groups such as the following:
<group> <state>Nebraska</state> <job>Deep Sea Fisherman</state> <avgincome/> </group>
I.3 Queries on SequenceXQuery uses the
<< and >>
operators to compare nodes based on document
order. Although these operators are quite simple, they
can be used to express complex queries for XML
documents in which sequence is meaningful. The first
two queries in this section involve a surgical report
that contains procedure,
incision, instrument,
action, and anesthesia
elements.
The following query returns all the
action elements that occur between the
first and second incision elements inside
the first procedure. The original document order
among these nodes is preserved in the result of the
query.
let $proc := /report/procedure[1] for $i in $proc//action where $i >> ($proc//incision)[1] and $i << ($proc//incision)[2] return $i
It is worth noting here that document order is
defined in such a way that a node is considered to
precede its descendants in document order. In the
surgical report, an action is never part
of an incision, but an
instrument is. Since the
>> operator is based on document
order, the predicate $i >>
($proc//incision)[1] is true for any
instrument element that is a descendant
of the first incision element in the
first procedure.
For some queries, it may be
helpful to define a function that can test whether a
node precedes another node without being its
ancestor. The following function returns
true if its first operand precedes its
second operand but is not an ancestor of its second
operand; otherwise it returns false:
declare function local:precedes($a as node(), $b as node())
as boolean
{
$a << $b
and
fn:empty($a//node() intersect $b)
};
Similarly, a local:follows function could be written:
declare function local:follows($a as node(), $b as node())
as boolean
{
$a >> $b
and
fn:empty($b//node() intersect $a)
};
Using the local:precedes function, we can write a
query that finds instrument elements between the first
two incisions, excluding from the query result any
instrument that is a descendant of the first
incision:
let $proc := /report/procedure[1] for $i in $proc//instrument where local:precedes(($proc//incision)[1], $i) and local:precedes($i, ($proc//incision)[2]) return $i
The following query reports incisions for which no prior anesthesia
was recorded in the surgical report. Since an anesthesia
is never part of an incision, we can use
<< instead of the less-efficient
local:precedes function:
for $proc in /report/procedure
where some $i in $proc//incision satisfies
fn:empty($proc//anesthesia[. << $i])
return $procIn some documents, particular sequences
of elements may indicate a logical hierarchy.
This is most commonly true of HTML. The following
query returns the introduction of an XHTML document,
wrapping it in a div element. In this example, we
assume that an h2 element containing the text
"Introduction" marks the beginning of the introduction,
and the introduction continues until the next h2
or h1 element, or the end of the document, whichever
comes first.
let $intro := //h2[text()="Introduction"],
$next-h := //(h1|h2)[. >> $intro][1]
return
<div>
{
$intro,
if (fn:empty($next-h))
then //node()[. >> $intro]
else //node()[. >> $intro and . << $next-h]
}
</div>Note that the above query makes explicit the hierarchy that was implicit in the
original document. In this example, we assume that the h2 element containing the text "Introduction" has no subelements.
I.4 Recursive TransformationsOccasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.
Suppose that we need to compute a table of contents for a given document by scanning over the document, retaining only elements named section or title, and preserving the hierarchical relationships among these elements. For each section, we retain subelements named section or title; but for each title, we retain the full content of the element. This might be accomplished by the following recursive function:
declare function local:sections-and-titles($n as node()) as node()?
{
if (fn:local-name($n) = "section")
then element
{ fn:local-name($n) }
{ for $c in $n/* return local:sections-and-titles($c) }
else if (fn:local-name($n) = "title")
then $n
else ( )
};The "skeleton" of a given document, containing only its sections and titles, can then be obtained by invoking the local:sections-and-titles function on the root node of the document, as follows:
local:sections-and-titles(fn:doc("cookbook.xml"))As another example of a recursive transformation, suppose that we wish to scan over a document, transforming every attribute named color to an element named color, and every element named size to an attribute named size. This can be accomplished by the following recursive function:
declare function local:swizzle($n as node()) as node()
{
typeswitch($n)
case $a as attribute(color)
return element color { fn:string($a) }
case $es as element(size)
return attribute size { fn:string($es) }
case $e as element()
return element
{ fn:local-name($e) }
{ for $c in $e/(* | @*) return local:swizzle($c) }
case $d as document-node()
return document
{ for $c in $d/* return local:swizzle($c) }
default return $n
};The transformation can be applied to a whole document by invoking the local:swizzle function on the root node of the document, as follows:
local:swizzle(fn:doc("plans.xml")) I.5 Selecting Distinct CombinationsIt is sometimes necessary to search through a set of data to find all the distinct combinations of a given list of properties. For example, an input data set might consist of a large set of order elements, each of which has the same basic structure, as illustrated by the following example:
<order> <date>2003-10-15</date> <product>Dress Shirt</product> <size>M</size> <color>Blue</color> <supplier>Fashion Trends</supplier> <quantity>50</quantity> </order>
From this data set, a user might wish to find all the distinct combinations of product, size, and color that occur together in an order. The following query returns this list, enclosing each distinct combination in a new element named option:
for $p in fn:distinct-values(/orders/order/product),
$s in fn:distinct-values(/orders/order/size),
$c in fn:distinct-values(/orders/order/color)
order by $p, $s, $c
return
if (fn:exists(/orders/order[product eq $p
and size eq $s and color eq $c]))
then
<option>
<product>{$p}</product>
<size>{$s}</size>
<color>{$c}</color>
</option>
else ()This log records the changes that have been made to this document since the Last Call Draft of 04 April 2005.
J.1 7 July 2005eq and ne are now defined for the xs:duration type.strip
(Rule 1-e-ii-C-II), when stripping the type of an attribute: If the name
of the attribute is xml:ID, then the "is-ID" property of the attribute
is set to True; otherwise False.preserve and copy-namespaces mode is no-preserve have been changed to introduce a new type error: XQTY0086. void is changed to empty-sequence.fn:subtract-dateTimes-yielding-dayTimeDuration becomes op:subtract-dateTimes
and fn:subtract-dates-yielding-dayTimeDuration becomes op:subtract-dates
(affects operator mapping table). J.2 15 September 2005xml:id have been modified. Additional normalization rules apply to these attributes. The error (XQST0082) that was raised when the value of an xml:id attribute was not a valid NCName has been deleted.node-name property of a constructed attribute node is xmlns or xmlns:*, regardless of how the node-name was computed.xdt:untypedAtomic into the appropriate numeric type. This change defines overflow and underflow behavior for numeric literals. J.3 03 November 2005 (CR Draft)order by clause), the relative URI is resolved against the base URI of the static context.| XML Editor | XML Author | WYSIWYG Editors | Schema Editor | XSD Documentation | XSL/XSLT Editor | XQuery | XML Databases | SVN Client © 2002-2011 SyncRO Soft Ltd. All rights reserved. | Sitemap | Terms of Use | Privacy Policy | This website was created & generated with <oXygen/>® XML Editor | ||