A data complexity and rewritability tetrachotomy of ontology-mediated queries with a covering axiom

06/07/2020

∙

by   Olga Gerasimova, et al.

∙

0

∙

share

Aiming to understand the data complexity of answering conjunctive queries mediated by an axiom stating that a class is covered by the union of two other classes, we show that deciding their first-order rewritability is PSpace-hard and obtain a number of sufficient conditions for membership in AC0, L, NL, and P. Our main result is a complete syntactic AC0//NL/P/coNP tetrachotomy of path queries under the assumption that the covering classes are disjoint.