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> -----Original Message----- > From: James Clark [mailto:jjc@j...] > Sent: Sunday, June 23, 2002 10:15 PM > To: Don Box; John Cowan > Cc: xml-dev@l... > Subject: Re: DTDs, W3C Schemas, RELAX NG, Schematron? > > > > > 5) RNG allows a (simple) datatype to be restricted not only by facet, > > > but by explicit extension and exception. One can write 'xsd:integer - > > > "0"' to mean a nonzero integer (although unfortunately "00" will still > > > validate), or 'xsd:integer | "Inf" | "+Inf" | "-Inf"' when a value may > > > be integral or infinite. > > > > Wow! I was knocked out by this one. What good are datatypes if one can > > [not] work in terms of the value space of the type rather than the > lexical > > form? > > In RNG, you can work in terms of the value space. If you want a non-zero > integer, you can say > > xsd:integer - xsd:integer "0" > > or > > <data type="integer"> > <except> > <value type="integer">0</value> > </except> > </data> Thanks for the clarification. This seems reasonable. > > I've found that the most important difference between RNG and XML > > Schemas is wrt the underlying type model. > > > > Specifically, XML Schema uses named types to implicitly convey intention > > as well as structure (a la Java, C++, C#). Anonymous types are 2nd class > > citizens in XML Schema (they're type-equivalent with nothing). > > > > Relax NG has a much looser model (a la Perl) in which two things are > > compatible if they share structure independent of a common, named type > > definition. > > > > Each approach appeals to its own community of users in very deep ways. > > I agree that the emphasis on named typing in W3C XML Schema is a profound > difference from RNG. One interesting question is whether it would be > possible to build a schema language that supports named typing yet still > has > (at least most of) the simplicity and power of RNG. I had this thought myself recently, but frankly, I think lack of named typing is RNG's primary attraction for most people. > However, I still have > my doubts that named typing is appropriate for XML. I would speculate > that > named typing is part of what makes use of DCOM and CORBA lead to the kind > of > relatively tight coupling that is exactly what I thought we were all > trying > to avoid by moving to XML. I admit that it's a very weird dynamic. Correct me if I'm wrong, but even with RNG, equivalence still relies on common element names unless wildcards are used everywhere, no? DB
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