Proposition: "SGML is Gumming Up the Works"

Mark Tucker mct at
Fri Sep 11 23:40:34 BST 1998


SGML is Gumming Up the Works, or
	Down with DTD's.  Long Live Schemas!


I wish I had a clean concscience. That I could say "I'm an SGML expert,
and I still believe ...." But I'm a newbie, and definitely NOT
an SGML expert.

Like "Samuel R. Blackburn" <sblackbu at>, I got interested
in XML not because it is a good document formatting language,
but on the promise that with XML, I can interchange Data!

I'm a computer scientist. I see XML-Data, and think: "Hey, there are
type definitions.  And hey, this data file clearly contains instances
of those types."  

But, stepping into the XML community, I'm overwhelmed by the SGML
history of XML.  I'm told: "No, conforming to type definitions isn't
good enough. That is not Real Validation. You must be valid according
to a DTD."  (Perhaps XML-DATA seems to have died because it wasn't
DTD-ish enough; I don't know.)

And then, looking at DTD's, I find that they aren't even as good as
BNF context free grammars. And BNF is much weaker than type systems,
which we need and want.

So, we end up jumping through hoops to write DTD's to express DATA
which is very, very, very easily described in terms of modern
programming language type systems.  All the while, hearing a low chant:
"What kind of cretin are you? You don't want to *validate* your data! (shock)
You only want well-formed documents." -- NO and YES.  I don't care
if my document can be validated by a pitiful DTD.  I do care that 
it conform to a real type schema!



I'm not really mad at XML but, I think "Richard L. Goerwitz III"
<richard at> is on to something in wondering if SGML
compatibility is going to bring down the XML effort.

If you have to be an SGML wizard to express easy things,
then we're in trouble.  

Much of the initial selling of XML was:
		You don't need DTD's to be a good citizen.

I hope we can honor that promise.

-- Mark

P.S. I'm optimistic about RDF, and am afraid that DCD sold out a bit towards
documents.  I want DATA schemas!


[Why DTD's aren't as good as BNF]

It's easier to have name clashes with
ELEMENT NAMES than it is to create ambigouous BNF grammars. Several
BNF productions can start with open paren 
		function f (a:int) return (a + 3);
All ELEMENT names must be unique.

Mark Tucker			tucker_m at
Regenstrief Institute		phone: (317) 630-2606
1001 W. 10'th St; Indianapolis, IN; 46202-2859;	fax: (317) 630-6962

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