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Re: DTD Fragments and XML

From: Paul Prescod <papresco@calum.csclub.uwaterloo.ca>
Date: Sat, 03 May 1997 16:28:42 -0400
Message-ID: <336B9FFA.9319ECAC@calum.csclub.uwaterloo.ca>
To: w3c-sgml-wg@w3.org
Terry Allen wrote:
> This is not Paul's main concern in this post.  To set the record straight,
> for Docbook you would construct a customization layer consisting of
> additional overriding parameter entities and associated stuff.  You
> wouldn't have to touch the DTD for most purposes.  However, Docbook's
> means of achieving this uses empty parameter entities, which I now
> understand to be invalid in XML.  I'll spend part of this weekend
> removing them from my XMLized version of 3.0, which is now called
> XDB 0.2 (available at http://www.sonic.net/~tallen/xdb02.zip).
> I'd welcome correction on this point, or suggestions for other
> methods of customization that are valid in XML.

Even if you get it working, I don't consider modifying parameter
entities and rewriting content models is a very easy way to add a single
element to a DTD. Inclusions may be evil in SGML, but the XML
alternative "just delete that DOCTYPE thing" seems worse to me.

As far as future-SGML goes, I'm thinking that it should be possible to 

 * extend the content model of an element whose existing content model
is a simple or-group, 

 * override an entity in a way that depends on the old entity,

 * (perhaps) prepend and append contents to a content model.

 * include content in some form of namespace.

But for XML I guess I would be happy with a standard syntax for
declaring the namespace that your elements come from:


You could "combine" DTDs by tagset-including more than one DTD. GI clash
will be a problem, but a solvable one. GI clash wil only be a problem
for the elements you actually use.

For this to be meaningful, there would have to be a conformance level 
between well-formedness and validity. We would advocate (or even 
require) that XML documents live in the upper two levels. 

I hope I've demonstrated that the space between well-formedness and 
validity is HUGE and that we will lose big if we force authors to 
choose between flexibility/accurate generic markup and declared 
gi-semantic conformance to standard DTDs.

 Paul Prescod
Received on Saturday, 3 May 1997 16:36:43 UTC

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