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[xsl] Pure Union Type


Subject: [xsl] Pure Union Type
From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sun, 4 May 2014 02:29:39 -0000

I am reading the XPath 3.0 Recommendation.

The definition of "pure union type" is:


 "[Definition: A pure union type is an XML Schema union type that
satisfies the following constraints: (1) {variety} is union, (2) the
{facets} property is empty, (3) no type in the transitive membership
of the union type has {variety} list, and (4) no type in the
transitive membership of the union type is a type with {variety} union
having a non-empty {facets} property].

Note:

The definition of pure union type excludes union types derived by
non-trivial restriction from other union types, as well as union types
that include list types in their membership. Pure union types have the
property that every instance of an atomic type defined as one of the
member types of the union is also a valid instance of the union type."

My Questions:
1. In the phrase: "The definition of pure union type excludes union
types derived by non-trivial restriction from other union types", what
is meant to be a "non-trivial restriction"?

2. Can somebody provide a meaningful example? For example, can we
define a "my:numeric" pure union type as the union of xs:decimal,
xs:integer, xs:float, xs:double, ..., etc ? If yes, could somebody
provide the XML Schema type definition of this pure union type?  I
believe that this type is absolutely necessary to use for the
arguments and results of functions (and operators) defined on numbers.


-- 
Cheers,
Dimitre Novatchev
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Truly great madness cannot be achieved without significant intelligence.
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