Inverse Roles Make Conjunctive Queries Hard

Abstract. Conjunctive query answering is an important DL reasoning task. Although this task is by now quite well-understood, tight complexity bounds for conjunctive query answering in expressive DLs have never been obtained: all known algorithms run in deterministic double exponential time, but the existing lower bound is only an EXPTIME one. In this paper, we prove that conjunctive query answering in ALCI is 2-EXPTIME-hard (and thus complete), and that it becomes NEXPTIME-complete under some reasonable assumptions.

• Type: Conference
• Year: 2007
• Where: DLOG
• Authors: Carsten Lutz
• Keywords: Automated Reasoning, Conjunctive Query Answering, DL Reasoning Task, DLOG 2007, Tight Complexity Bounds