Parser compliance

Marcus Carr mrc at
Thu Nov 18 03:53:58 GMT 1999

David Megginson wrote:

> The DTD has two small but important roles in system implementation: as
> a partial set of structural validation rules and as a partial schema
> for guided authoring (it's nearly always supplemented in both cases).


> Unfortunately, SGML consultancies who knew mainly just DTDS and FOSIs
> were substituting DTD design for data analysis, domain modelling,
> system design, user interface design, and lots of other things for
> which DTDs are woefully inadequate.

Also agreed. However very few SGML people would have used a DTD in domain modelling, system
design or user interface design, so inadequacies in those areas equal SGML's inability to
deliver milk to your doorstep. :-) I don't deny for a second that the ability to base systems
on XML without DTDs is an extremely good thing - it will almost surely make XML the defining
force in computing. The fact remains though that for documents that were created against a
DTD, it is incorrect to declare that it is a myth that validation can tell you what's wrong
with your XML. Depending on the structure (tiny, all empty elements) and the data (must be
tokens from attribute lists), validation may be a perfectly adequate method of uncovering
problems. The further you move from this model, the more you need to supplement the
information availabe from the DTD, as you pointed out above.

> DTDs should have been just part of the solution, not *the* solution.

I still don't see what the other part should have been. It still sounds as though there was
some sort of willful conspiracy or ignorance, but it appears to be based on the fact that we
can do so much more now, so we should have known better then.

> In any case, my message was an explanation of why DTDs have been so
> heavily hyped, not an attack on the idea of DTDs themselves.  DTDs
> were the great Golden Hammer of the SGML consulting world.

Yes, when nails were the only thing that held houses together.


Marcus Carr                      email:  mrc at
Allette Systems (Australia)      www:
"Everything should be made as simple as possible, but not simpler."
       - Einstein

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