As is oft noted, DTDs serve different purposes in the production
process.
Thinking beyond single applications, where a DTD exists, the file can
be proved valid. This is a legal concept as much as a computer science
technology. Different tools for different purposes indeed.
We create standards to serve both human and computer processes.
Correct-by-construction techniques are well-understood. The trust they
provide in computer communications is established. Where content has
longer
lifecycles and the intent of the *author* is part of the information to
be
maintained, the abstract schema is a useful form of contracting, hence,
the
BNF in the specifications.
While there are efforts to replace the SGML schemata syntax, some effort
should be given to extending it. As requirements are developed for
the alternatives, I suggest that the working group for SGML make the
same effort for SGML DTDs as the requirements there have a different
emphasis.
Len Bullard