The following compilation lists a few web sites that are relevant to schema definition in XML.
The World Wide Web Consortium (W3C) is the reference point for the XML specification (i.e. DTDs) and XML Schema.
http://www.xml.org/ (hosted by OASIS)
is a repository for XML schemas.
discusses programming techniques for schema authors.
contains a collection of design patterns for XML.
is the home of Asset Oriented Modeling.
