Approximating OWL-DL ontologies

Efficient query answering over ontologies is one of the most useful and important services to support Semantic Web appli-cations. Approximation has been identified as a potential way to reduce the complexity of query answering over OWL DL ontologies. Existing approaches are mainly based on syntac-tic approximation of ontological axioms and queries. In this paper, we propose to recast the idea of knowledge compila-tion into approximating OWL DL ontologies with DL-Lite ontologies, against which query answering has only poly-nomial data complexity. We identify a useful category of queries for which our approach guarantees also complete-ness. Furthermore, this paper reports on the implementa-tion of our approach in the ONTOSEARCH2 system and pre-liminary, but encouraging, benchmark results which compare ONTOSEARCH2’s response times on a number of queries with those of existing ontology reasoning systems