Reto pointed me to the Jena Semantic Web Toolkit [1] which has some RDF-specific APIs and query language implemented. Jena is part of HP Labs Semantic Web Research [2].

via Reto Bachmann-Gmuer, private email

[1] http://www.hpl.hp.com/semweb/jena.htm
[2] http://www.hpl.hp.com/semweb/index.htm