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The need for a formal description

• To: xml-dev@l...
• Subject: The need for a formal description
• From: Gustaf Liljegren <gustaf.liljegren@b...>
• Date: Tue, 19 Aug 2003 02:01:35 +0200

I've been trying to understand just *why* the Schema WG is working on the
"XML Schema: Formal Description" document. I remember James Clark
criticized [1] WXS for the lack of integrating this formal description in
the spec from the start:

<quote>
More than a year after the publication of the W3C XML Schema
Recommendation, "XML Schema: Formal Description" [4] is still a work
in progress and is still far from being a complete and correct
description of the semantics of XML Schema; moreover, it cannot be
relied on as it has no normative force.

The RELAX NG formalism has a solid basis in tree automata theory.  W3C
XML Schema has no such basis.

The role of a schema in a specification is to serve as a formalism.
How good is a formalism if that formalism itself lacks a proper formal
basis?
</quote>

Still, I have seen enough successful standards based on DTDs, and does DTDs
have a formal description? Well, I think the description is formal enough,
but I guess there's must be something lacking, because the RNG spec and the
formal description for WXS looks all different.

If it's so important to have a formal description, why hasn't the document
made any progress since 2001? I found this quote [2] from Jonathan Robie,
that suggests that if it was completed today, it would define a slightly
different standard:

<quote>
Personally, I would like to see us finish the Formal Description, make 
it normative, and make XML Schema agree with it.
</quote>

Finally, was the idea of a formal description for WXS inspired by Relax NG
or is it obvious that any schema language needs it?

Gustaf

--
1. http://www.imc.org/ietf-xml-use/mail-archive/msg00217.html
2. http://lists.w3.org/Archives/Public/www-xml-schema-comments/
   2002JanMar/1103.html

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