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Validation API, was: Regarding the vote on XML Schema.

On 24/04/2001 07:06:48 Rick Jelliffe wrote:

>Merely saying "XML Schemas bad!  RELAX good!" keeps the cart before the
>horse.  If there is no modularity or ability to plug-n-play with different
>kinds of schema, then every little engineering trade-off has to be subjected
>to exhaustive discussion (as in XML Schemas) with no guarantee that the
>result will satisfy everyone.

Agreed.  What would help us more is a validation API that allows pluggable
validators, and that allows (multiple) validation of any part of an XML
document, not just the whole document.  If your Schema wraps a legacy DTD, why
shouldn't the legacy tags be validated using the DTD?  If you have validation
code in your application (and there is always some, doing the things that
DTDs/Schemas can't do), separate it out and build your own pluggable validator.
That will make your application architecture cleaner.

My major concern in achieving this is that Schemas can be applied to a DOM tree
(which is very nice), but I'm not sure what tricks there might be in trying to
do the same with DTDs, which were not designed with that in mind.  Of course,
you would want not just these two, but also TREX/RELAX, Schematron, and any
other likely suspects that might come along.

All of this said, is anyone else interested in being able to do this kind of
thing, or is it all too hard?  My impression is that for a lot of the world,
DTDs are the now, XML Schemas will do what most people need for the future
(remembering that most people aren't on the "xml-dev" list ...), and anything
else tends to be marginalised as a toy for XML weenies.  The existence of a good
API could change that (just as SAX and DOM made XML parsers accessible and
acceptable by removing the lock-in), but I'm interested to know whether the rest
of you see things the same way.  All comments gratefully received.

Anthony B. Coates
Leader of XML Architecture & Design
Chief Technology Office
Reuters Plc, London.

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