mapping a relational database as RDF

A user has a large volume of data stored in a traditional RDBMS, and
currently queries that data using SQL.

The user wishes to expose an RDF view of the the database. The user
should be able to translate his SQL queries into RDF queries with very
little need for additional custom code.

This clearly isn't really a use case in its own right; it's starting a
level higher at the abstract requirements.

Is there any support for such a requirement? Is it worth working up a
few use cases which include RDBMS schema, their RDF translations, and
the SQL queries that we'd like to be able to translate?