Query Rewriting under EL TBoxes: Efficient Algorithms

We propose a new type of algorithm for computing firstorder (FO) rewritings of concept queries under EL-TBoxes that is tailored towards efficient implementation. The algorithm outputs a non-recursive datalog rewriting if the input is FO-rewritable and otherwise reports non-FO-rewritability. We carry out experiments with ontologies from practical applications which show that our algorithm performs very well in practice, and that EL-TBoxes originating from real-world applications admit FO-rewritings (of reasonable size) in almost all cases, even when in theory such rewritings are not guaranteed to exist.