A note on refinement operators

Abstract

The top down induction of logic programs is faced with the problem of ensuring that the search space includes all the desired hypotheses. The conventional way of of organizing the search space is via refinement of clauses. Within this context the existence of a well behaved refinement operator complete for Horn clause logic is desirable. We show that there is no natural way in which a complete refinement operator can be defined which avoids the production of non-reduced clauses. Consideration is given to subsets of full Horn clause logic for which more efficient refinement operators can be constructed.