DTD vs DCD vs Schema

Rick Jelliffe ricko at allette.com.au
Tue Jan 19 02:41:19 GMT 1999

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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