A Query Tool for EL with Non-monotonic Rules

We would like to thank Miguel Calejo for his help with InterProlog, Pavel Klinov for his help with ELK, Terry Swift for his help with XSB, and Gonca Gullu for her collaboration. Vadim Ivanov was partially supported by a MULTIC – Erasmus Mundus Action 2 grant. Matthias Knorr and Joao Leite were partially supported by FCT funded project ERRO – Efficient Reasoning with Rules and Ontologies (PTDC/EIA-CCO/121823/2010) and Matthias Knorr also by FCT grant SFRH/BPD/86970/2012. We present the Protégé plug-in NoHR that allows the user to take anEL+⊤ontology, add a set of non-monotonic (logic programming) rules – suitable e.g. to express defaults and exceptions – and query the combined knowledge base. Our approach uses the well-founded semantics for MKNF knowledge bases as underlying formalism, so no restriction other than DL-safety is imposed on the rules that can be written. The tool itself builds on the procedureSLG(O)and, with the help of OWL 2 EL reasoner ELK, pre-processes the ontology into rules, whose result together with the non-monotonic rules serve as input for the top-down querying engine XSB Prolog. With the resulting plug-in, even queries to very large ontologies, such as SNOMED CT, augmented with a large number of rules, can be processed at an interactive response time after one initial brief pre-processing period. At the same time, our system is able to deal with possible inconsistencies between the rules and an ontology that alone is consistent.