& XSLT >  so, new feature, new tag.

But one tag

<constraint test="(XQuery|XPath expression)"/> 

should be enough - not 3000 tags.
>  
>  > 
>  > Can you give me an example of a constraint which is difficult, or 
>  > verbose, to express in a declarative language such as XQuery?
>  
>  Here is one that you can't express in W3C XML Schema :
>  -the number of cells must be the same in all columns of the 
>  table http://reflex.gforge.inria.fr/tutorial/active-schema/datas.xml

Yes, but it's still easy to express declaratively:

<constraint test="count(distinct-values(table/count(column)) = 1"/> 

>  
>  If this discussion were reduced to schemata, a language such 
>  as XQuery could be used to express additional constraints 
>  that you can't express with your favorite schema language ; 
>  this is the same as using Schematron, or by using XSLT for 
>  further validation. However, none of them act at the 
>  component level, that is to say at the content model level : 
>  an editor would propose you to insert an element which would 
>  be rejected by XQuery/Schematron/XSLT.

Yes, grammars are good for that; it's hard to reproduce that in a
predicate-based constraint language.

Michael Kay
 


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