A defeasible logic reasoner for the semantic web

Defeasible reasoning is a rule-based approach for efficient reasoning with incomplete and inconsistent information. Such reasoning is, among others, useful for ontology integration, where conflicting information arises naturally; and for the modeling of business rules and policies, where rules with exceptions are often used. This paper describes these scenarios and reports on the implementation of a system for defeasible reasoning on the Web. The system, DRDEVICE, is capable of reasoning about RDF metadata over multiple Web sources using defeasible logic rules. It is implemented on top of CLIPS production rule system and builds upon RDEVICE, an earlier deductive rule system over RDF metadata that also supports derived attribute and aggregate attribute rules. Rules can be expressed either in a native CLIPS-like language, or in an extension of the OO-RuleML syntax. The operational semantics of defeasible logic are implemented through compilation into the generic rule language of R-DEVICE. The paper also presents a full semantic Web broker example for apartment renting.