Efficient Query Answering over Fuzzy EL-OWL Based on Crisp Datalog Rewritable Fuzzy EL++

OWL EL is an extension of the tractable EL description logic. Despite their inference capabilities over TBoxes, DL reasoners have a high ABox reasoning complexity which may constitute a serious limitation in the Semantic Web where we rely mainly on query answering (i.e. instance checking). The subsomption algorithm used in fuzzy EL reduce instance checking into concept satisfiability. To allow efficient instance checking and query answering over fuzzy EL-OWL, we propose in this paper two approaches for integrating fuzzy EL and crisp Datalog programs: homogenous and hybrid approaches. In the homogenous approach, we define crisp EL rules based on a crisp rewriting of fuzzy EL. To preserve decidability, crisp EL rules are then written with Datalog safe ones. In the hybrid approach, fuzzy EL axioms and assertions are defined with EDB facts and Datalog rules are used to denote fuzzy EL instance checking deduction rules. That is, DL axioms and assertions are translated into Datalog EDB facts and Datalog rules are used to derive conclusions about them.