relational mapping?

Has anyone come across a mapping of the relational model to RDF? I'm sure
there's a pretty direct one possible at a low level (tuple to tuple I
suppose), but it'll save me some thought and a lot of time if someone's
already looked into this. Alternatively, if there's an RDFS around that
contains RDBMS terms (schema, table, column etc) I'd very much like to hear
about it. I'm wanting to operate at this latter level, but it would be nice
to be on firm foundations.

Cheers,
Danny.

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Danny Ayers
http://www.isacat.net