SquirrelRDF is quite similar to our D2RQ. There’s a lot of data out there, but much is not in RDF, but in databases. SquirrelRDF allows SPARQL queries against databases.
Mapping from DB schema to RDF is done along the lines described in 1998 by TBL. The mapping is created automatically by a small tool that introspects the database schema. Mappings are 1:1 from table to class and from column to property.
It’s a simple tool – the hard work is down by Jena’s ARQ query engine which breaks down SPARQL queries into much simple triple queries and passes them to SquirrelRDF.
Should be available as a Jena contrib Real Soon Now. (Update: It’s released.)