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   RE: Proposal Announcement - XML DTDs to XML docs

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  • From: "Simon St.Laurent" <SimonStL@classic.msn.com>
  • To: "Xml-Dev (E-mail)" <xml-dev@ic.ac.uk>
  • Date: Thu, 21 May 98 01:05:58 UT

Paul Prescod wrote:
>> 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.
>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?

At what level do you get defaulted attributes now?  Do you get defaulted 
attributes in a well-formed document without a DTD?  Right now, it doesn't 
look like it.  This could be in level 1, if default attributes were deemed 
necessary to document syntax, but I'd expect to see it in level 3.  Internal 
entities could be defined much as they are now, at the start of a document, 
within a structure set aside for that purpose using <ENTITY> (or whatever 
develops) instead of <!ENTITY>.  This would indeed need to be covered in level 
1, unless you could live without internal entities.  In the past you seemed 
quite happy about forcing scripts to be external to a document, so I can't see 
why it would be so terrible to exile entities - and DTDs as well - to separate 
documents either.  I don't think it would be necessary, though, any more than 
it's necessary now.

As for requiring levels, level 1 would serve a similar purpose to well-formed 
documents today.  2 would be a prerequisite for 3, of course.

>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 think this is overstating your case rather dramatically.  I could do 
something similarly brutal by creating a <? shorttags ?> PI at the start of a 
regular XML document and using the implied tags.  No one else could read my 
documents, but I sure could.  Not only that, but I already proposed separating 
the document syntax - which includes full start- and end-tags - from the DTD.  
There's no reason this proposal would allow the DTD to modify the basic 
document syntax and markup, period.

>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. 

We can argue about the meaning of the word schema all you like; it's not that 
exciting for me.  XML-Data performs similar mapping, but attempts to add a lot 
more, parts which I see more as data schemas.  If this is a schema, then so be 

>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.

My suggestion is that DTD's present a significant problem in their current 
format, and that they could be improved significantly.  I would enjoy being 
able to focus on elements and attributes, the core of XML (and SGML) document 
syntax, and worry less about the rest.  This project already is an attempt to 
be smaller, but to provide a place for new things to grow.

Simon St.Laurent
Dynamic HTML: A Primer / XML: A Primer / Cookies

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