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   RE: [xml-dev] Interesting mailing list & a rare broadside

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Title: RE: [xml-dev] Interesting mailing list & a rare broadside
You could be right but DTDs aren't terribly complicated and they got a bum
rap from the web community for years until the bums learned how to use
them.  That is the typical approach to the learning curve; to spit like
camels in the general direction of the drivers.

As to having multiple schema languages, I don't see a reason why not.
With the exception of DTDs, these are all XML application languages
and if someone were to say that we need the consortia to eliminate
competitors there, I think a lot of us would ignore such advice the same
way the procurement officials will ignore the Beltway crowd that issues
opinions such as "W3C standards only".  If you've done much of this
kind of work, you may remember when it was "ISO only" or "NIST only"
and so on.  The ocean of innovation beats down any barrier one can
put up and the results are that houses built on cliffs loose that
exclusive view and sometimes disappear into the swells.
Specifications and standards must stand on their technical merits,
not their provenance.   Trust yourselves to figure out what is best
for your own applications.   Those that really need to interoperate
will negotiate.  Those that don't don't need your technology. The
best advice I have for anyone just getting into this is to avoid
people who tell you that you must first "create buzz" before
you have a working product, or that getting tight with the W3C,
those of standing, whoever, is the first order of business.  Those
with standing recognize good work and will be a lot happier to
see you coming with running code than a handful of brochures.
The rules haven't changed:  running code and rough consensus
are the best predictors of survival.

From: Anderson, John [mailto:John@Barbadosoft.com]

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.


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