Constraint Patterns for Tractable Ontology-Mediated Queries with Datatypes.

© 2016, CEUR-WS. All rights reserved. Adding datatypes to ontology-mediated conjunctive queries (OMQs) often makes query answering hard. This applies, in particular, to datatypes with non-unary predicates. In this paper we propose a new, non-uniform way, of analysing the data-complexity of OMQ answering with datatypes containing higher-arity predicates. We aim at a classification of the patterns of datatype atoms in OMQs into those that can occur in non-tractable OMQs and those that only occur in tractable OMQs. Our main result is a P/coNP-dichotomy for OMQs over DL-Lite TBoxes and rooted CQs using the datatype (ℚ, ≤). The proof employs a recent dichotomy result by Bodirsky and Kara for temporal constraint satisfaction problems.