First Order-Rewritability and Containment of Conjunctive Queries in Horn Description Logics / 965
Meghyn Bienvenu, Peter Hansen, Carsten Lutz, Frank Wolter

We study FO-rewritability of conjunctive queries in the presence of ontologies formulated in a description logic between EL and Horn-SHIF, along with related query containment problems. Apart from providing characterizations, we establish complexity results ranging from ExpTime via NExpTime to 2ExpTime, pointing out several interesting effects. In particular, FO-rewriting is more complex for conjunctive queries than for atomic queries when inverse roles are present, but not otherwise.

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