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Subject: Re: ID/IDREF problem
James Clark wrote: > > In addition to ID/IDREF, XML Schemas Part 1 has a new facility for > identity-constraints (using the xsd:unique, xsd:key, xsd:keyref, > xsd:selector, xsd:field elements). See > http://www.w3.org/TR/xmlschema-1/#Identity-constraint_Definition_details). > This is quite a good facility. The only thing I think it lacks is > proper support for hierarchical references. On the other hand the > elements supporting identity-constraints have the feel of a separate > language, which could easily be layered on top of the rest of Schema > Part 1. There is another limitation: IMO, it would be much more powerful if the paths in these mechanism were defined as being XPath expressions than being defined as paths pointing to nodes from the document. > We could support these XML Schema Part 1 elements for identity > constraints in TREX by allowing <element> elements to have arbitrary > elements from other namespaces with a global attribute > trex:role="constraint". Just like you can plug in a datatyping language > to TREX, so you would be able to plug in a identity-constraint language. More generally, wouldn't it be possible to plug a rule checking language ? Identity constraints can be seen as rules. Eric -- Rendez-vous à Paris pour net2001. http://www.mynet2001.net/pgmonline2001/it2.html ------------------------------------------------------------------------ Eric van der Vlist Dyomedea http://dyomedea.com http://xmlfr.org http://4xt.org http://ducotede.com ------------------------------------------------------------------------
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