Queries in object-oriented datab;Lqcs are formulated against a class and retrieve instnnccls of the class sat,isfying a certain predicate on the att,riblltes of the class. The presence of a class hierarchy, an integral part of any object-oriented data model, allows answers to be expressed implicitly in terms of classes and instances. This enables answers to be provided at different levels of ion. Shum and Muntz [SM88] presented a way of providing implicit expressions based on a taxonomy defined over the database. The algorithm presented in [SM88] is optimal in the length of the answer but the clarity of the answer is often poor. In this paper, the focus is on coherent answers: implicit answers that are not necessarily optimal in the number of terms but are easy to comprehend. We show that a uniqlle coherent answer can be obtained efficiently in a top down nlanncr. Since the objective is to provide cohcrcnt, answers, and user queries are formulated by means of query operators to access...
Hava T. Siegelmann, B. R. Badrinath