Set Tabulation Tuple Tabulation ?

This paper investigates a tuple-oriented approach to tabulation. In this approach solutions to a call are stored and computed one at a time, which results in tables contain incomplete sets of solutions. Since the answers stored in the tables are partial sets of solutions to a call, a subgoal that is an instance of a stored call can require an answer that is not among the stored solutions. Consequently recomputation can arise. This recomputation problem is overcome by introducing a program transformation. Evaluation in the transformed program is free of recomputation because it is diverted from previously visited search space, corresponding to previously computed and stored solutions in the tables. In this paper we also show that negation and tabulation can be eeciently implemented under this approach. The advantages and the problems that emerge with this proposal are discussed.