Loss of effective schema validation by DTDs with today's working
Curt.Arnold at hyprotech.com
Mon Sep 27 23:27:07 BST 1999
One of the things that has been troubling me with today's schema working
draft release is the reduction of the effectiveness of validating a schema
with the schema DTD. For example, in the previous draft, an element with an
empty content model was represented by
The <empty> element was defined as having an empty content model, so the
following fragment would result in a validation error.
In todays, draft the same thing poorly formed element would be represented
and would validate.
Also, the <datatype> element definition in the schema for datatypes uses the
"all" compositor (equivalent the SGML &) which allows each of the different
facets to appear once, but in any order. Since the all compositor was not
included in XML, the closest a DTD can do is allow any of the elements to
appear in any order any number of times. It would seem better for the
schema to define a specific order so that the DTD could enforce the number
of times a particular facet appears.
The changes appear intentional from the previous draft and I'm sure there is
reasoning (and probably a huge amount of debate) behind it. However, I
really liked the <choice>, <sequence>, <any> and <empty> tags from the
previous public draft.
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