Contextualized Knowledge Repositories with Justifiable Exceptions

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 Knowledge 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 programs with negation under answer set semantics. The translation generates datalog 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 description logics and contextual knowledge representation.