I don't think that there need be any hard decisions about the interaction
of XSchemas and DTDs. They are two different types of schemas they need
not have any effect on each other at all. If there is a DTD present, and
the user has a validating parser, the user can validate against the DTD.
If there is a schema present, and the user has an XSchema processor, the
user can validate against the XSchema.
If the DTD is algorithmically derived from the XSchema, then the document
is guaranteed to pass both tests if it passes the XSchema. Otherwise each
test is performed and reported separately by the appropriate software.
Paul Prescod - http://itrc.uwaterloo.ca/~papresco
Three things are most perilous: Connectors that corrode
Unproven algorithms, and self-modifying code
http://www.geezjan.org/humor/computers/threes.html