A logical toolbox for ontological reasoning

In ontology-enhanced database systems, an ontology on top of the extensional database expresses intensional knowledge that enhances the database schema. Queries posed to such systems are to be evaluated considering all the knowledge inferred from the data by means of the ontology; in other words, queries are to be evaluated against the logical theory constituted by the data and the ontology. In this context, tractability of query answering is a central issue, given that the data size is normally very large. This paper surveys results on a recently introduced family of Datalog-based languages, called Datalog+/-, which is a useful logical toolbox for ontology modeling and for ontology-based query answering. We present different Datalog+/- languages and related complexity results, showing that Datalog+/- can be successfully adopted due to its clarity, expressiveness and its good computational properties.