Synthesizing extensional constraints in Ontology-based Data Access

Several recent techniques and tools for Ontology-based Data Access (OBDA) make use of the so-called extensional constraints (a.k.a. ABox dependencies). So far, extensional constraints have been mainly considered in a setting where data are represented in an ABox, instead of external data sources connected to the ontology through declarative mappings. Moreover, the issue of how to generate extensional constraints in practice has not been addressed yet. In this paper we first provide a formal account of the notion of extensional constraints in a full-fledged OBDA setting, where an ontology is connected to the data sources of the information system by means of mappings, and then present an approach to the automatic generation of extensional constraints in such a setting. The technique we propose is based on the use of a first-order theorem prover that checks validity of relevant formulas built over the mapping views. The experiments we have carried out in real-world OBDA projects show the effectiveness of our approach in discovering large collections of extensional constraints entailed by the OBDA specification.