R.V. Guha's rdfDB. Intended to be a simple, scalable, open-source
database for RDF. Written in C and based on top of the Sleepycat
Berkeley Database, it supports interrogation via TCP/IP sockets,
meaning integration is possible with any programming language.

rdfDB uses a high level SQLish query language. The data is modelled as
a directed labelled graph (RDF).

The goals of this project are to build a database that is capable of:

   1. Supporting a graph oriented API via a textual query language ala
      SQL.
   2. Load/Reload an RDF file from a url into the database
   3. Scalable to millions of nodes and triples.
   4. Provide support for RDF Schemas.
   5. Provide support for some basic forms of inferencing.
   6. Provide both C and Perl access to the database.
   7. The Perl philosophy applies : Simple things should be simple and
      complex things should be possible.

WWW: http://www.guha.com/rdfdb/