Efficient Query Rewriting in the Description Logic EL and Beyond.

We propose a new type of algorithm for computing first-order (FO) rewritings of concept queries under ELHdr-TBoxes. The algorithm is tailored towards efficient implementation, yet complete. It outputs a succinct non-recursive datalog rewriting if the input is FO-rewritable and otherwise reports non-FO-rewritability. We carry out experiments with realworld ontologies which demonstrate excellent performance in practice and show that TBoxes originating from applications admit FO-rewritings of reasonable size in almost all cases, even when in theory such rewritings are not guaranteed to exist.