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Re: XQuery and DTD/Schema?


bray xquery schema
At 09:31 AM 7/3/2002 -0700, Tim Bray wrote:
>At the moment this latter assumes that the schema validation is done by 
>XSD because as far as I can tell nobody ever asked for the ability to use 
>a different validation facility.  I see no architectural reason why you 
>couldn't add an argument or environment variable or something 
>saying  "here's the identifier of the schema language I'm using".
>
>It's going to be tough to tear XQuery away from XML Schema's base data 
>types, and probably not worth doing; they ain't perfect but the code to 
>deal with them is written and out there, so why fight it.  Note that XSD 
>base types are effectively built-in to RELAX software too these days.
>
>Beyond that, I see no architectural difficulty in making XQuery 
>schema-language agnostic.  -Tim

Making a query language agnostic with respect to the underlying model is 
fairly difficult, and the devil is in the details.

RELAX-NG uses purely structural typing. XML Schema uses named typing, as 
does XQuery (for the most part).

There is no problem supporting RELAX-NG as well-formed XML with datatypes, 
but you would have to define a mapping that creates type annotations for 
the simple types. If you want XQuery to support the structure of elements, 
you would have to create type annotations for these as well. I think all of 
this could be done, but this would require someone to sit down and do a 
fair amount of work.

There are some aspects of RELAX-NG which XQuery would not support, such as 
co-occurrence constraints.

Jonathan


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