CoBase: a cooperative database system*

Abstract

Abstract This chapter proposes the use of the type abstraction hierarchy (TAH) as a framework for deriving cooperative query answers (CQA). The TAH integrates abstraction with the subsumption (is-a) and composition (part-of) semantics found in the type hierarchy. This framework provides a multi-level object representation that is an important aspect of cooperative query answering. Patterns, which specify one or more conditions on an object, are introduced as a small granularity structure with specific semantic information. Cooperative query answering uses the TAH and patterns to provide query relaxation, generalization, and specialization. Relaxation can be explicitly controlled by the user, implicitly performed by the system, or both. An explanation system is also included to present the relaxation path, as well as a nearness measure between the approximate answer and the exact answer.