Web Things, by Mark Baker

Norm asks;

Given a random XML document, one of the things you might want to know about it is, “What is an appropriate schema to apply”? Now, for DTDs, this is a simple question: look at the document type declaration. If it has one, the public and system identifiers will tell you what DTD to apply; if it doesn’t have one, there’s no DTD to apply.

Sounds like a job for RDDL.