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Re: [xml-dev] "vocabulary constraints" and other constraints (was:Re: [xml-dev] RE: Difference between "normalize" and "canonicalize"?)

On Fri, 27 Feb 2009 19:34:49 -0700, C. M. Sperberg-McQueen wrote:
> If you believe that the boundary between what a schema language should
> do and what it should not do is always clear, then it's no wonder you
> confused people.  Particularly since pretty much every schema language
> ever used with XML does more than constraining the presence or absence
> of particular elements and attributes, so none of them sticks with
> what you now seem to be saying is their only real business.

XPath/XSLT attribute content syntax cannot be expressed without a 
"datatype" language defined as a full context-free grammar.

Granted, there's not *much* parity in XPath expressions, but what's 
there is inescapable.  Any expression that can contain a function can't 
be validated by any of the existing "datatype" languages, the most 
expressive of which is at best defined by a regular grammar (and 
pattern support in WXS is a rather begrudging concession, expressed as 
a facet on a "real" datatype).

Amelia A. Lewis                    amyzing {at} talsever.org
Confidence: a feeling peculiar to the stage just before full
comprehension of the problem.

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