DR-Prolog: A System for Reasoning with Rules and Ontologies on the Semantic Web

Antonis Bikakis, Grigoris Antoniou

Abstract: The development of the Semantic Web [Berners Lee et al., 2001] proceeds in layers, each layer being on top of the others. At present, the highest layer that has reached sufficient maturity is the ontology layer in the form of the description logic based languages, DAML+OIL and OWL. The next step in the development of the Semantic Web will be the logic and proof layers. Rule systems can play a twofold role in the Semantic Web initiative: (a) they can serve as extensions of, or alternatives to, description logic based ontology languages; and (b) they can be used to develop declarative systems on top (using) ontologies. Defeasible reasoning is a simple rule-based approach to reasoning with incomplete and inconsistent information. It can represent facts, rules, and priorities among rules. Its main advantage is the combination of enhanced representational capabilities allowing one to reason with incomplete and contradictory information, coupled with low computational complexity compared to mainstream nonmonotonic reasoning . In this paper we report on the implementation of a defeasible reasoning system for reasoning on the Web. Its main characteristics are the following: (a) It is compatible with RuleML (details in full paper); (b) It is based on Prolog. The core of the system consists of a well-studied translation [Antoniou et. al., 2001] of defeasible knowledge into logic programs under Well-Founded Semantics [van Gelder et al., 1991]; (c) The main focus is on flexibility. Strict and defeasible rules and priorities are part of the interface and the implementation. Also, a number of variants are implemented (ambiguity blocking/propagation, conflicting literals); (d) The system can reason with rules and ontological knowledge, through the transformation of the RDFS constructs and many OWL constructs into rules.