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RE: X-Schema

• From: Ronald Bourret <rbourret@i...>
• To: "XML Developers' List" <xml-dev@i...>
• Date: Wed, 16 Jun 1999 17:33:23 +0200

David Hunter wrote:
> I'm just
> wondering if we wouldn't be better off adding the extra functionality to
> DTDs, instead of creating a new language.  Are there technical reasons 
why
> we can't?  (Does it have something to do with SGML compatibility?  If so 
I'd
> be willing to shut up right now.  :-)

There are certainly no technical barriers to enhancing DTDs.  As you point 
out, though, SGML compatibility is a barrier.  Mostly it's always struck me 
as a matter of practicality: there are very few DTD writers and readers 
compared to the number of document writers and readers.  Hence, the market 
is most likely to lean towards documents, not DTDs.  If we redefine/extend 
DTDs as documents (i.e. schemas), we get to use all the document technology 
and tools for free.  If we work solely on DTDs, we have to reinvent 
everything ourselves: SAX for DTDs, DOM for DTDs, XSLT for DTDs, editors 
for DTDs, etc.

As to DTDs becoming obsolete, I view this as very unlikely to occur any 
time soon. More likely are two things:

1) Parsers that can translate between DTDs and schemas on the fly so that 
it becomes unimportant whether a document has one or the other, and

2) Separate modules that can validate documents against a schema for use in 
environments where the parser either can't validate or can't validate 
against a DTD.

-- Ron Bourret


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