Parser compliance

Marcus Carr mrc at
Thu Nov 18 00:08:56 GMT 1999

David Megginson wrote:

> 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.

Are you suggesting that we would have done the client a favour by disregarding structure and
steering them toward a good word processor? It's a bit disingenuous to criticise what was far
and away the best solution at the time. It was no more or less a money-grab than the current

> 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.

Surely you're not suggesting that structure is less important if you have semantically correct
data? The two go hand in hand, revealing different yet related aspects of the document. I
don't see the distinction.

> 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.

That has always been the case - it's never been enough just to make the document valid. Not in
SGML and not in XML. The diminished requirement for a DTD in XML doesn't diminish the need for
structure - we're just assuming that control might rest with some other mechanism. The fact
that we're getting more control over the data contents of elements is fantastic, as it has
always been required, but it doesn't change the fact that something has to understand the
structure too. I think that this thread is turning into a simple rewrite of history.


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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