Design of the Tableau Reasoner TGC2 for Description Logics

Abstract

Ontologies have been applied in a wide range of practical domains. They play a key role in data modeling, information integration, and the creation of semantic web services, intelligent web sites and intelligent software agents. The Web ontology language OWL, recommended by W3C, is based on description logics (DLs). Automated reasoning in DLs is very important for the success of OWL, as it provides support for visualization, debugging, and querying of ontologies. The existing ontology reasoners are not yet satisfactory, especially when dealing with qualified number restrictions and large ontologies. In this paper, we present the design of our new reasoner TGC2, which uses tableaux with global caching for reasoning in E xpTime-complete DLs. The characteristic of TGC2 is that it is based on our tableau methods with the optimal ( ExpTime) complexity, while the existing well-known tableau-based reasoners for DLs have a non-optimal complexity (at least NExpTime). We briefly describe the tableau methods used by TGC2. We then provide the design principles of TGC2 and some important optimization techniques for increasing the efficiency of this reasoner. We also present preliminary evaluation results of TGC2. They show that TGC2 deals with qualified number restrictions much better than the other existing reasoners.