On the Web Ontology Rule Language OWL 2 RL

It is known that the OWL 2 RL Web Ontology Language Profile has PTime data complexity and can be translated into Datalog. However, a knowledge base in OWL 2 RL may be unsatisfiable. The reason is that, when translated into Datalog, the result may consist of a Datalog program and a set of constraints in the form of negative clauses. In this paper we first identify a maximal fragment of OWL 2 RL called OWL 2 RL with the property that every knowledge base expressed in this fragment can be translated to a Datalog program and hence is satisfiable. We then propose some extensions of OWL 2 RL and OWL 2 RL that still have PTime data complexity.