Transforming XML content into RDF assertions

As a newcomer to this list, who reviewed its archives in only a cursory
fashion, I have a question about the practical conversion of XML content
into an RDF knowledgebase?

If one has a collection of XML documents sharing one or more XML Schemas and
an RDF Schema describing the knowledgebase structure, how would they proceed
to populate the knowledgebase?  Is there a tool that helps one build an
executable mapping between an XML Schema and an RDFS or DAML+OIL schema?
Are there examples where useable knowledgebases have been realized in this
manner?

Thanks for any guidance.

Michael Denny