Query by Class, Rule and Concept

M. Staudt, H.W. Nissen, M.A. Jeusfeld

	   The ideal query language for a knowledge base will probably
	   never be found: easy formulation and easy evaluation of
	   queries are two conflicting goals. Easy formulation asks
	   for a flexible, expressive language near to human language
	   or gestures. The second goal requires an effective mapping
	   to machine code which computes the correct answer in a
	   finite number of steps. This paper approaches the problem
	   by a query language with three faces. The first one projects
	   queries to concepts of the knowledge representation language
	   KL-One for easy formulation and readability. The second
	   face presents queries as rules of a deductive database with
	   fixpoint semantics. Finally, queries appear as classes whose
	   instances are the materialized answer (view) to the query.
	   The methods for maintaining and updating the views are compiled
	   from their deductive interpretation.