Similarity and metrics in case-based reasoning

Similarity is a core concept in case-based reasoning (CBR), because case base building, case retrieval, and even case adaptation all use similarity or similarity-based reasoning. However, there is some confusion using similarity, similarity measures, and similarity metrics in CBR, in particular in domain-dependent CBR systems. This article attempts to resolve this confusion by providing a unified framework for similarity, similarity relations, similarity measures, and similarity metrics, and their relationship. This article also extends some of the well-known results in the theory of relations to similarity metrics. It appears that such extension may be of significance in case base building and case retrieval in CBR, as well as in various applied areas in which similarity plays an important role in system behavior. © 2002 Wiley Periodicals, Inc.