Next: About this document

CoBase: A Cooperative Database System

Wesley W. Chu, Qiming Chen and Matthew Merzbacher
Computer Science Department
University of California at Los Angeles


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.

The operations required for CQA may be added to any conventional query language. As an example, we present CSQL, a cooperative extension of SQL used in the CoBase project at UCLA. Experimental results reveal that the proposed type abstraction hierarchy and relaxation control provide an organized structure for representing concepts at different knowledge levels in various domains, and offers a systematic and efficient method for cooperative query answering.

Index Terms: Knowledge Representation, Type Hierarchy, Type Abstraction Hierarchy, Query Language, Query Rewrite, Cooperative Query Answering, Semantic Distance, Relaxation Control

View the Paper (requiri ng a postscript viewer)
Tue Jun 21 15:38:40 PDT 1994