Using Tabled Logic Programming to Solve the Petrobras Planning Problem

ABSTRACT. Tabling has been used for some time to improve efficiency of Prolog programs by memorizing answered queries. The same idea can be naturally used to memorize visited states during search for example in planning. In this paper we present a planner developed in the Picat language to solve the Petrobras planning problem. Picat is a novel Prolog-like language that provides pattern matching, deterministic and non-deterministic rules, and tabling as its core modeling and solving features that are very appropriate for solving planning problem. We demonstrate these capabilities using the Petrobras domain, where the goal is to plan transport of cargo items from ports to platforms using ships with limited capacity. This domain has been introduced in the Fourth International Competition on Knowledge Engineering for Planning and Scheduling (ICKEPS 2012) as a challenge real-life motivated problem. Monte Carlo Tree Search was so far the best technique to tackle this problem and we will show that by using tabling we can achieve comparable efficiency.