QUERY BY CLASS, RULE, AND CONCEPT

The ideal query language for a knowledge base will probably never be f ound: easy formulation and easy evaluation of queries are two conflict ing goals. Easy formulation asks for a flexible, expressive language n ear to human language or gestures. Easy evaluation of queries requires an effective mapping to machine code, which computes the correct answ er in a finite number of steps. This article approaches the problem by a query language with three faces. The first projects queries to conc epts of the knowledge representation language KL-One for easy formulat ion and readability. The second presents queries as rules of a deducti ve database with fixpoint semantics. The third presents queries as cla sses whose instances are the materialized answer (view) to the query. The methods for maintaining and updating the views are compiled from t heir deductive interpretation.