DLDB: Extending Relational Databases to Support Semantic Web Queries

We present DLDB, a knowledge base system that extends a relational database management system with additional capabilities for DAML+OIL inference. We discuss a number of database schemas that can be used to store RDF data and discuss the tradeoffs of each. Then we describe how we extend our design to support DAML+OIL entailments. The most significant aspect of our approach is the use of a description logic reasoner to precompute the subsumption hierarchy. We describe a lightweight implementation that makes use of a common RDBMS (MS Access) and the FaCT description logic reasoner. Surprisingly, this simple approach provides good results for extensional queries over a large set of DAML+OIL data that commits to a representative ontology of moderate complexity. As such, we expect such systems to be adequate for personal or small-business usage.