On ontology-based data access

In my talk, I am going to discuss recent results on the computational complexity of answering conjunctive queries to databases via ontologies. Such queries are known to be first-order rewritable over ontologies formulated in the OWL 2 QL profile of the Web Ontology Language OWL 2 and various dialects of Datalog$+{}-$. I analyse both the worstcase size and the “real-world” practical size of such rewritings and discuss some emerging problems.