xml editor

[Zearin]

I'm trying to write a Relax NG Compact schema. RNC syntax is an absolute dream compared to XSD, and I like it better than regular RNG, too. But I'm trying to do something that's a little tricky.

I'm trying to write a schema that defines the elements <courses> and <course>. Basically, I want to be able to specify optional attributes on <courses>, but if specified disallows the attributes on nested <course> elements.

For example, the following would be legal:

Code: Select all

<courses dept="ENGL">
<course number="101" />
<course number="201" />
</courses>

And the following would also be legal:

Code: Select all

<courses>
<course dept="ENGL" number="101" />
<course dept="ENGL" number="201" />
</courses>

But the following should be illegal:

Code: Select all

<courses dept="ENGL">
<course dept="ENGL" number="101" />
<course dept="ARTT" number="201" />
</courses>

…Because if <courses> has specified a @dept, no contained elements should be allowed to specify @dept of their own. (The idea is that they "inherit" their parent's @dept value.)

Does anyone know how to write this in Relax NG Compact syntax? (If not, does anyone have any advice?)[/code]

[Dan]

Here it is the schema in Relax NG compact syntax that defines the <courses> element as a choice. I named the root element <test>:

Code: Select all

default namespace = ""
start =
  element test {
     element courses {
       (
           attribute dept { xsd:NCName },
           element course {
             attribute number { xsd:integer }
           }+
       ) |
       (
         element course {
           attribute dept { xsd:NCName },
           attribute number { xsd:integer }
         }+
       ) 
     }+
  }


The XML I have used to test it was derived from your examples:

Code: Select all

<?oxygen RNGSchema="relaxNgTest.rnc" type="compact"?>
<test>
    <!-- Valid -->
    <courses dept="ENGL">
        <course number="101"/>
        <course number="201"/>
    </courses>

    <!-- Valid -->
    <courses>
        <course dept="ENGL" number="101"/>
        <course dept="ENGL" number="201"/>
    </courses>

    <!-- Not Valid -->
    <courses dept="ENGL">
        <course dept="ENGL" number="101"/>
        <course dept="ARTT" number="201"/>
    </courses>
</test>


Best regards,
Dan

[Zearin]

Thanks.

However, I was looking to utilize one of Relax NG Compact's abilities to redefine elements. Your example is a workable solution, but these two elements are just one pair among many that I want to write, and writing out the complete definition for each context would get pretty tiresome.

I know about the include directive and its ability to redefine elements, but what I'm fuzzy on is how to redefine an element in as efficient a manner as possible.

For example, let's say I have the following named patterns (capitalized for easy identification):

Code: Select all

Courses = element courses {
   Course+
}
Course = element course { course.attlist }
course.attlist =
   attribute dept         {text}?,
   attribute number      {text},
   attribute credits      {xsd:nonNegativeInteger}?,
   attribute grade         {xsd:string{minLength="1" maxLength="2"}}?,
   attribute title         {text}?,
   attribute description   {text}?


Now, according to the Relax NG Compact tutorial, there's a way to say "everything but" by using a minus operator. Then there is also the notAllowed keyword.

But whenever I try to use either, the validator lights up with errors. (And as although I am very happy with Oxygen, the errors for RNG Compact files don't explain the problem at all. I know RNG Compact isn't XML, but it's designed to be 1-to-1 compatible with XML, which should theoretically allow the editor to provide more helpful tooltips…)

So continuing the example above, what I would like to do is something sort of like the following… (this is invalid, but I'm just trying to communicate what I'm trying accomplish)

Code: Select all

Courses = element courses {
   (
      attribute dept {text},
      Course {attribute dept = notAllowed}+
   ) |
   Course+
}
Course = element course { course.attlist }
course.attlist =
   attribute dept         {text}?,
   attribute number      {text},
   attribute credits      {xsd:nonNegativeInteger}?,
   attribute grade         {xsd:string{minLength="1" maxLength="2"}}?,
   attribute title         {text}?,
   attribute description   {text}?


[Zearin]

I thought of another way to write my last codeblock that might make slightly more sense (though still invalid ):

Code: Select all

Courses = element courses {
   (
      attribute dept {text},
      Course = element course {course.attlist - attribute dept}
   ) |
   Course+
}
Course = element course { course.attlist }
course.attlist =
   attribute dept         {text}?,
   attribute number      {text},
   attribute credits      {xsd:nonNegativeInteger}?,
   attribute grade         {xsd:string{minLength="1" maxLength="2"}}?,
   attribute title         {text}?,
   attribute description   {text}?


[Dan]

Unfortunately, you cannot use the minus operator. It is intended only for use with name classes, not with patterns. I spent some time trying to find a correct way of rewritting a pattern similar to the one you suggested, but the results were more complicated that the basic solution of using a choice.

(Another solution for such a problem would be Relax NG in XML syntax and embedded Schematron rules, but I am not sure if it is acceptable for you..)

[Zearin]

Thank you.

Damn. I was afraid that was the case.

Relax NG XML syntax isn't bad, and isn't off-limits for any technical reason. I'm just using RNG Compact for easy of writing & reading. I love what XML can do, but all those pointy angular brackets sure do get to be a burden on the eyes, sometimes…

Just out of curiosity, do you (or anybody else?) know why one can't use the minus operator with patterns?

My gut feeling is that if you can name a pattern, and if you can use an operator on a named pattern, you should be able to use an operator on any pattern. (But I'm not clever enough to invent syntaxes, so I can't figure that one out on my own.)