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Subject: Re: ID/IDREF problem
James Clark wrote: > > Eric van der Vlist wrote: > > > > 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. > > I don't understand your point. In the XML Schema CR, the paths are > general XPath expressions. (This is going to change to a very, very > restricted subset of XPath.) There are some situations where it would be useful to use a XPath function instead of a XPath expression pointing to a node in the tree. One example are references to fragments in the same document: <author id="jclark"> ... <product name="xt"> <author xlink:type="simple" xlink:href="#jclark"/> ... The match could be done if the keyref path allowed "substring-after(@xlink:href, '#')", the result of a XPath expression that doesn't point to anything in the document. This would be useful to handle other cases of compounded keys where a reference is not stricly equal to a key of composed with the key. > > > > 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. > > Yes. Allowing arbitrary expressions can be seen as a first step to write context dependent rules... Eric > James -- 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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