Practical approach to knowledge base verification

We consider verifying knowledge bases to three levels of rigor: detection of anomalies, verification of safety properties, and verification of full correctness. We present formal definitions for four classes of anomalies which may be present in knowledge bases expressed using first order logic: redundancy, ambivalence, circularity and deficiency. The definitions are initially given for rule-based systems without uncertainty, but we extend them to consider uncertainty and frame-based knowledge representations. We demonstrate that, although verification of full correctness will not usually be feasible for knowledge-based systems, it is important that their safety properties be verified, and we present a method for doing this based on our definitions of logical anomalies. We demonstrate the validity of this framework by presenting the results of a verification performed on the knowledge base of a working expert system.