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   RE: [xml-dev] FW: [ANN]: XQuery: A Guided Tour

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At 10:26 AM 9/30/2003, Dare Obasanjo wrote:
>As for XQuery being able to support other XML schema languages in future, 
>this is nice but I'm curious as to what exactly this means in practical 
>terms. The working group already has seen the problems caused when one 
>group builds a "type system" (and I use the term loosely) which they 
>believe can work for some future language only for their assumptions to 
>come out wrong. I originally was of the mind that this was a laudable goal 
>of XQuery and still think it is a laudable goal to have it in the data 
>model but wonder how feasible it is to actually create an XQuery 
>implementation with what is basically a "pluggable" type system. A 
>validation language with pluggable datatypes (which are basically custom 
>checking on string values) like RELAX-NG has is fairly straightforward 
>enough but a creating a pluggable type system where you have to deal with 
>issues like type promotion & type substitutability is a bit harder.

I think that the data types of XML Schema Part 2 would have to be a given. 
But this is the most common set of types used in RELAX-NG as well.

On the other hand, validation in XQuery is pretty much a black box. 
Currently, we import W3C XML Schemas, and validation is defined by that 
spec. But there's nothing to say we couldn't import a different kind of 
schema and use that for validation, as long as the named types are properly 
assigned, and the built-in atomic types of W3C XML Schema are the ones used 
for simple types.



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