Approximate Evaluation of Logic Programs

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Extension tables are a memo structure for logic programs that save the extension of a predicate in a table. Subsequent calls, whose answers are in the table, use a table lookup rather than recomputing the results. Since the terms that are saved are not necessarily ground facts, the induced subsumption ordering on Prolog terms is used to avoid saving redundant information in the table. This duplicate elimination mechanism will be extended by allowing for the specification of orderings other than those given by the subsumption of Prolog terms. This enhanced capability modifies the behavior of the execution method to provide an approximate evaluation of the logic program based on these orderings.