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   RE: [xml-dev] XQuery and DTD/Schema?

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At 05:09 PM 7/6/2002 -0700, Dare Obasanjo wrote:
 > Mike Champion wrote:
> > and I've never heard anyone but Jonathan want the ability to ensure 
> that the results of
> > a query are valid instances of a schema without running them through a 
> validator.

XQuery can't guarantee schema validity completely, because it does not 
model all of XML Schema (eg it does not model identity constraints or 
facets), and because there are cases in which the type information used is 
not specific enough. It *can* catch a large number of common errors.

>That's probably because most people realize that this problem is beyond 
>the ability of computer science to solve and even for decidable cases may 
>be expensive to implement or utilize.


No static typing system is complete. However, static typing is very useful, 
and is widespread in working systems. It just makes sense to report errors 
as early as you can, and to use type information for optimization.



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