EL-ifying Ontologies

ABSTRACT. The OWL 2 EL profile is a fragment of the ontology language OWL 2 for which standard reasoning tasks are feasible in polynomial time. Many OWL ontologies, however, fall outside the EL profile and hence profile-specific reasoners are not applicable. Such ontologies, however, typically contain a small number of axioms outside EL, which may have little or no influence on reasoning outcomes. In this paper, we investigate techniques for rewriting non-EL axioms into EL that preserve the outcomes of classification and instance queries and which are applicable to the DL SHOIQ. Furthermore, for Horn ontologies, we devise a technique inspired by EL-reasoning that can be used to reduce the size of pre-models in (hyper)tableau reasoning. We have implemented and extensively tested our techniques with very encouraging results.