> 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
