Controlling the Search in Tabled Evaluations

SLG has proven to be an efficient and elegant strategy to evaluate normal logic programs with respect to the well-founded semantics. Given the flexibility tabling provides in the choice of when to schedule answers, efficiency of evaluation can be further improved by choosing an appropriate scheduling strategy, that is, how and when answers are returned to consuming nodes. Several different scheduling strategies for SLG have been investigated including a set-at-a-time strategy well-suited for accessing relations in external databases. This paper explores Local Scheduling, a strategy that by following the dependencies among subgoals during evaluation, simplifies the computation of the well-founded model of programs with negation, and avoids non-productive computation in the presence of answer subsumption (e.g., in aggregate computation and abstract interpretation). Even though Local Scheduling performs well in general, there are cases where it leads to unacceptable performance --- the sa..