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   Re: Proposal Announcement - XML DTDs to XML docs

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  • From: Paul Prescod <papresco@technologist.com>
  • To: "Xml-Dev (E-mail)" <xml-dev@ic.ac.uk>
  • Date: Wed, 20 May 1998 20:08:03 -0400

Simon St.Laurent wrote:
> It's good to get feedback.
> 1) A document syntax specification (a simplified version of well-formed
> documents)
> 2) A syntax for linking to DTDs (and perhaps schemas) internal or external
> (which would depend on XLink)
> 3) A syntax for DTDs providing rules for validation.
> (Schema definitions could rest on top of #3 or beside it.)

So at what level do I get the equivalent of internal entities and
defaulted attributes? And what levels are required of all XML processors
vs. optional?
> I would certainly want this to be extensible; parsers that didn't understand
> an extended portion of this DTD could simply ignore that portion, provided the
> document met the basic rules.  

The important point is that you aren't talking about an alternate notation
for XML DTDs, but a complete change in the relationship between DTDs and
documents. In XML, DTDs can affect the interpretation (not just
validation) of a document, through entities, defaulted attributes,
element-content vs. mixed-content and so forth. If DTDs can both change
the way a document is parsed *and* be extensible, then two parsers could
get completely different information out of the same document.

For example: One company's DTD extension could add in SGML tag ommission.
The start- and end-tag of an element could be implied, without violating
well-formedness. So then you could use that company's parser through SAX
and get a completely different set of events than if you used someone
else's parser. After all, changing the parse is one of the
responsibilities of the DTD.

> I would rather _not_ provide full schema information in this
> proposal - moving XML DTDs to a new format seems like enough of a task to
> start with.

I don't know what you mean by full schema information. DTDs serve as
schemas (in addition to changing the parse). If you propose to replace
DTDs, then you are in part designing a new schema language. My suggestion
is to develop a new schema language *without* changing DTDs. In other
words, I am suggesting you make your project smaller, not larger. I would
suggest you forget about entities, defaulted attributes, etc. Leave those
to DTDs.

Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

"A writer is also a citizen, a political animal, whether he likes it or 
not. But I do not accept that a writer has a greater obligation 
to society than a musician or a mason or a teacher. Everyone has
a citizen's commitment."  - Wole Soyinka, Africa's first Nobel Laureate

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