DTD vs DCD vs Schema

David LeBlanc whisper at accessone.com
Tue Jan 19 03:23:06 GMT 1999

After perusing comp.text.xml, I was reminded that xml is a proper subset of
sgml and thus whence came dtds etc. I guess it would be hard to do away
entirely with dtds and retain that relationship.

My question was originally prompted by a desire to make provision in (ok,
yet another) xml parser (in C++) i'm starting work on for future
developments wrt dcd/schema etc. Maybe I can make the dtd parser pluggable.

Seems to me that the below idea of something complementing dtds rather then
replacing them is a good one.


Dave LeBlanc

At 01:42 PM 1/19/99 +1100, Rick Jelliffe wrote:
>From: Steven R. Newcomb <srn at techno.com>
>>The important thing is to go forward, and to avoid going backward,
>>with respect to the set of semantics that are expressible using DTDs.
>Personally, I don't think that compatability with what DTDs can model
>should be any constraint on a schema language, at least as far as
>content models.
>The current content model syntax is
>    * terse
>    * easy to read and write
>    * functional for a wide class of documents
>    * standard and well-understood
>    * part of XML
>    * fragment-friendly (SGML's global inclusions and exclusions
>have been removed)
>I would much prefer the schema system to assume to existance of a
>DTD, and provide the missing parts. For example,
>    1) a set of data types for attributes and elements
>    2) use XSL patterns to assert that if one pattern is found,
>then another pattern must exist.
>The second in particular gets us out of the content-model approach
>and into a "partial validation" approach which is more in tune with
>Rick Jelliffe
>ricko at gate.sinica.edu.tw

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