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Title: RE: [xml-dev] Interesting mailing list & a rare broadside
This rather nicely demonstrates the need for multiple schema languages.
If XML Schema had the ability to specify allowed root nodes, it would become even more complex (you'd need to also be able to specify root *types* as well, I think, & perhaps that a given element may only be the root if it has a particular attribute & <xsd:any namespace="http://www.w3c.org/2002/hideouslyComplexSchemaRules" /> ).
If RELAX provided some inheritance support (putting aside arguments as to whether a schema language should or not), it would start to become more complex.
If either of these languages provided support for complex co-constraints, things would get out of hand.
Schematron allows you to define allowed roots for a schema, and I dare say it won't be long before someone devises a streaming Schematron processor, so by combining the required features of different schema languages, all kinds of things are possible. It's also IMHO a much neater way to specify things like key/keyref relationships.
I think they called it component based development in the 90's. XSD doesn't have to be complex, regarless of verbosity, so perhaps the answer is to try to refactor it as a set of modular features, which you can specify as being supported or not in a schema or a processor (I'd personally always turn off complex type restriction).
I don't believe XSD is inherently evil (except with a hangover on a Monday morning), any more than the Dutch tax laws are (which are also hideously complicated and subject to multiple interpretations, though some would argue that *all* tax laws are evil) and it has some useful stuff. It would be nice to see XSD V2.0 heading towards simplification - maybe even <heresy>interoperable with RELAX NG</heresy> where each of the languages focuses on it's core competency as a component in a possible whole. However, having never designed a schema language, I have no idea if this is either possible or desirable.
From: Bullard, Claude L (Len) [mailto:email@example.com]
Sent: 05 June 2002 21:55
To: 'Elena Litani'; Simon St.Laurent
Subject: RE: [xml-dev] Interesting mailing list & a rare broadside
Wouldn't it have been better to provide something
analogous to DOCTYPE support where
is explicit rathen than relying on syntactic
position which may be accidental?
From: Elena Litani [mailto:firstname.lastname@example.org]
Xerces doesn't provide a way to specify a validation root, thus the
assumption is that the first element encountered by the
XMLSchemaValidator is the validation root.
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