The key idea is that RDBMSs in practice appears to indicate only that answering data, 'stored in a standard relational database management real-world queries over real-world databases turns out to be system (RDBMS), can be queried through an OWL 2 QL tractable. As rewritings can turn a standard query to something ontology via a simple rewriting mechanism, i.e., by rewriting'out of this world,' a first rule of thumb could be as follows: the query into an SQL query that is then answered by the rewritten query should look similar to the original the RDBMS, without any changes to the data' (

The use of ontologies for accessing data is one of the most exciting new applications of description logic in databases and other information systems. A realistic way of realising sufficiently scalable ontology- based data access in practice is by reduction to querying relational databases. In this paper, we describe the ‘combined approach,’ which incorporates the information given by the ontology into the data and employs query rewriting to eliminate spurious answers. We illustrate this approach for ontologies given in the DL-Lite family of description logics and briefly discuss the results obtained for the EL family.