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   Schema/DTD transitions (was Re: W3C XML Schema Questionaire)

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  • From: "Simon St.Laurent" <simonstl@simonstl.com>
  • To: Paul Prescod <paul@prescod.net>, xml-dev@xml.org
  • Date: Sun, 09 Jul 2000 08:34:31 -0400

At 01:58 AM 7/9/00 -0500, Paul Prescod wrote:
>Michael Brennan wrote:
>> I strongly agree with the above statement. Too many parties have tried to
>> get version 1.0 of the schema spec to solve too many problems. I think the
>> vast majority of developers just want the DTD functionality in XML syntax
>> with stronger data types now and are willing to wait for the other stuff as
>> they better digest the implications.
>Many of the complex features in XML Schema are intended to emulate
>sophisticated uses of DTDs. XML Schema will have a whole new problem if
>competent DTD designers will not move to Schemas because they are not as
>powerful as DTDs.

I'm not quite sure I get this.  Is your concern that:
1) Using XML syntax limits you to general, rather than parameter entities
2) The use of general entities is more restrictive (or at least 
	differently restrictive) than parameter entities
3) To make up for that shortfall, and its potential impact on 
	'competent' (I'd read 'advanced') DTD designers, Schemas
	needs a lot complex features

I can't quite figure out any other reason that Schemas 'need' complex

I've been pondering how XHTML 1.1 modularization will look in Schemas for a
while now, and its use of parameter entities is both sophisticated and
daunting.  While I think it will be possible to convert it to Schemas, the
current mismatch between the DTD parameterization approach and the
inheritance model that seems to be necessary for implementing the same
structures in Schemas is a big leap.

Hopefully, the XHTML 1.1 crew will start releasing the schema appendices,
and let us know how this should look - to me, that'd be a solid sign of how
to compare complex DTDs and Schemas.  (Heck, any drafts would be nice, as
it's been six months since the appearance of the Last Call draft.)

Simon St.Laurent
XML Elements of Style / XML: A Primer, 2nd Ed.
http://www.simonstl.com - XML essays and books

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