This paper describes a resolution based Description Logic reasoning system called DLog. DLog transforms Description Logic axioms into a Prolog program and uses the standard Prolog execution for efficiently answering instance retrieval queries. From the Description Logic point of view, DLog is an ABox reasoning engine for the full SHIQ language. The DLog approach makes it possible to store the individuals in a database instead of memory, which results in better scalability and helps using description logic ontologies directly on top of existing information sources. To appear in Theory and Practice of Logic Programming (TPLP).
In this paper, we present a brief overview of Pellet: a complete OWL-DL reasoner with acceptable to very good performance, extensive middleware, and a number of unique features. Pellet is the first sound and complete OWL-DL reasoner with extensive support for reasoning with individuals (including nominal support and conjunctive query), user-defined datatypes, and debugging support for ontologies. It implements several extensions to OWL-DL including a combination formalism for OWL-DL ontologies, a non-monotonic operator, and preliminary support for OWL Rule hybrid reasoning. Pellet is written in Java and is open source. Practical description logic systems play an evergrowing role for knowledge representation and reasoning research even in distributed environments. In particular, the often-discussed semantic web initiative is based on description logics (DLs) and defines important challenges for current system implementations. Recently, several standards for representation languages have been proposed (RDF, OWL). By introducing optimization techniques for inference algorithms we demonstrate that sound and complete query engines for semantic web representation languages can be built for practically significant query classes. The paper introduces and evaluates optimization techniques for the instance retrieval problem w.r.t. the description logic SHIQ(Dn)-, which covers large parts of OWL. The paper discusses practical experiments with the description logic system RACER. This paper reports on a pragmatic query language for Racer. The abstract syntax and semantics of this query language is defined. Next, the practical relevance of this query language is shown, applying the query answering algorithms to the problem of consistency maintenance between object-oriented design models.