Query answering under existential rules --- implications with existential quantifiers in the head --- is known to be decidable when imposing restrictions on the rule bodies such as frontier-guardedness. Query answering is also decidable for description logics, which further allow disjunction and functionality constraints (asserting that certain relations are functions); however, they are focused on ER-type schemas, where relations have arity two. This work investigates how to get the best of both worlds, having decidable existential rules on arbitrary arity relations, while allowing rich description logics, including functionality constraints, on arity-two relations. We first show negative results on combining such decidable languages. Second, we introduce an expressive set of existential rules (frontier-one rules with a certain restriction) which can be combined with powerful constraints on arity-two relations while retaining decidable query answering. Further, we provide conditions to add add functionality constraints on the higher-arity relations.

Accepted at IJCAI 2015. 7 pages.

© 2015 Antoine Amarilli and Michael Benedikt.