Parser compliance

David Megginson david at
Wed Nov 17 22:39:15 GMT 1999

Tim Bray <tbray at> writes:

> I have often wondered where this myth arose that validating against
> a DTD will tell you, in useful real-world terms, "what's wrong with
> your XML".

That's probably a rhetorical question, but for those new to the field
(i.e. who didn't come from SGML), SGML consultancies throughout the
1990's made an enormous portion of their money writing (and rewriting
and rerewriting and rererewriting) massive and incomprehensible DTDs
for government, military, and big industry, so naturally they (OK,
"we") hyped the importance of DTDs as the cornerstone of any system.

In XML, I've noticed that most of my consulting work has to do with
designing running systems and integrating components, and that
document-type design is only a small (though important) part of that.

In brief, then, SGML systems tend to be DTD-centric while XML systems
tend to be component-centric.  There's nothing in SGML or XML that
forces that distinction; it's just the way things fell out.  Tim's
right -- DTD-based validation will tell you only a tiny portion of
what's wrong with your document, though that portion can be helpful
in some circumstances.

All the best,


David Megginson                 david at

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