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Re: XML Schema becomes a W3C Recommendation

Rick Jelliffe wrote:
> From: Eric van der Vlist <vdv@dyomedea.com>
> >RSS 1.0 can't be described by W3C XML Schema (nor by a DTD).
> >A W3C XML Schema on RSS 1.0 would have been incompatible with 2 of our
> >requirements:
> >1) Simplicity: W3C XML Schema would have imposed an order on elements.
> >2) Modularity: you can't say that you want to allow any element from any
> >namespace from undeclared modules with W3C XML Schema.
> This brings up the old question of whether a schema defines or models (the
> "document type declaration" versus "document type definitions" issue.) If we
> say that the schema models the requirement (i.e., there may be some
> constraints which are not checked) then an XS schema certainly can made for
> RSS.

Exactly. We have taken the opposite approach where we believe that our
requirement must constrain the schema languages we will use.

Also it's not only a matter of constraints not being checked, but of non
constraints on element order being imposed.

> It is like the early claim that a DTD could not be made for RDF. However, a
> DTD fragment certainly could, and the ANY declared content type model some
> elements nicely.


I can use a xsd:any to specify that I want any namespace except the
target namespace, but here we need to exclude all namespaces of the
approved modules and that's not possible with W3C XML Schema.  
> I am not up-to-date with RSS recently: can RELAX and TREX cope with its
> model OK?  I believe Schematron can.

Yes, it should be possible to define RELAX, TREX, Schematron and
examplotron schemas for RSS.

> Cheers
> Rick Jelliffe
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See you in Hong Kong for www10:
Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
http://xsltunit.org      http://4xt.org           http://examplotron.org