RE: mapping a relational database as RDF "I'm currently working on an extended version of D2R MAP called D2RQ, which will allow the general rewriting of RDQL and find(s,p,o) queries to database specific SQL queries.
I have attached the current language specification and an example mapping which shows how the ISWC ontology (http://www.wiwiss.fu-berlin.de/suhl/bizer/d2rmap/iswc.daml.xml) is mapped
to a corresponding application specific relational schema (http://www.wiwiss.fu-berlin.de/suhl/bizer/d2rmap/iswc.sql.txt). The example also shows how D2RQ deals with taxonomical class structures in the ontology and many-to-many relationships in the data base.
D2RQ is currently implemented as a plug-in for Jena 2.1. The first prototype will be released sometime in May under an open source license."