Query optimization in object-oriented knowledge bases

摘要

We define an object-oriented knowledge base to be a deductive knowledge base that is based on an object model. One of the major advantages provided by object-oriented knowledge bases is that the first order language used for object description can be used as a query language as well. Since object-dependent procedures are included in this framework, the problem of query processing is nontrivial. On one hand some attributes involved in a query need to be derived from a procedure and constrained by some other relations, and therefore combinatorial explosion may occur; on the other hand a query may be specified in an improper order such that the search space becomes intolerable large. In this paper we first describe two approaches to optimize the query evaluation process: the semantic optimization approach and the conjuct reordering approach. Next, we examine the problem of logical query processing when an object-oriented knowledge base is built on a relational database such as Ingres.