DR-DEVICE is capable of reasoning about RDF metadata over multiple Web sources using defeasible logic rules. The system is implemented on top of CLIPS production rule system and builds upon R-DEVICE, 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 most important features of DR-DEVICE are the following: * Support for multiple rule types of defeasible logic, such as strict rules, defeasible rules, and defeaters. * Support for both classical (strong) negation and negation-as-failure. * Support for conflicting literals, i.e. derived objects that exclude each other. * Direct import from the Web of RDF ontologies and data as input facts to the defeasible logic program. * Direct import from the Web of defeasible logic programs in an XML compliant rule syntax (RuleML). * Direct export to the Web of the results (conclusions) of the logic program as an RDF document.
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