Contextualized Knowledge Repositories with Justifiable Exceptions

Abstract. Representation of context dependent knowledge in the Semantic Web has been recognized as a relevant issue: as a consequence, a number of logic based formalisms have been proposed in this regard. In response to this need, in previous works, we presented the description logic-based Contextualized Knowl-edge Repository (CKR) framework. Starting from this point, the first contribution of the paper is an extension of CKR with the possibility to represent defaults in context dependent axioms and a translation of extended CKRs to datalog pro-grams with negation under answer sets semantics. The translation generates dat-alog programs which are sound and complete w.r.t. instance checking in CKRs. Exploiting this result, we have developed as a second contribution a prototype implementation that compiles a CKR based on OWL2RL to a datalog program. Finally, we compare our approach with major non-monotonic formalisms for de-scription logics and contextual knowledge representation.