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At 03:49 PM 1/4/01 -0500, Mike.Champion@SoftwareAG-USA.com wrote:

>DTDs are too limited to be used effectively for "data", but never heard that
>XSDs are not fully suitable for "documents".
>Clearly the XHTML entity declarations would have to be in a DTD (since 
>there is no way to declare entities in XSD), but in other ways would an 
>XSD and a DTD version of a document "schema" (broadly defined) be 

The issue is post-declaration arbitrary changes to content models.

I have module A, B, C, D, E, and F, which have the basic content models of 
Block, Inline, Flow, etc.

New Module Z is introduced and combined with A-F to create a new Host 
Language Conformant Document Type, where the foo element created in Z must 
be inserted in Block, or some other content set that's been pre-defined in 
another module.

With DTDs, this is done with heavy parameterization and the use of PEs such 
as %Block.extra which are defined as empty when the initial Block entity is 
defined, and can then be altered in the new modules to hold these additions.

Schemas, to the best of our understanding, don't provide this facility -- 
though there's been suggestion that there's a way, but the one person that 
understands it hasn't had the time to explain it, making it an unproven 

We could instantiate a real rathole if we discussed why Schemas are 
incapable of entity declarations in the first place, which has lead to 
questions of "why bother" if so much DTD segments must be used to replicate 
the facilities of XHTML to begin with.


Ann Navarro, Author and Chief Geek
WebGeek, Inc. http://www.webgeek.com
Now Available! - XHTML By Example -