Planning systems have become an important tool for automating a wide variety of tasks. Control knowledge guides a planner to find solutions quickly and is crucial for efficient planning in most domains. Machine learning techniques enable a planning system to automatically acquire domain-specific search-control knowledge for different applications. Past approaches to learning control information have usually employed explanation-based learning (EBL) to generate control rules. Unfortunately, EBL alone often produces overly complex rules that actually decrease rather than improve overall planning efficiency. This paper presents a novel learning approach for control knowledge acquisition that integrates explanation-based learning with techniques from inductive logic programming. In our learning system SCOPE, EBL is used to constrain an inductive search for control heuristics that help a planner choose between competing plan refinements. SCOPE is one of the few systems to address learning control information for newer, partial-order planners. Specifically, this proposal describes how SCOPE learns domain-specific control rules for the UCPOP planning algorithm. The resulting system is shown to produce significant speedup in two different planning domains, and to be more effective than a pure EBL approach.
Future research will be performed in three main areas. First, SCOPE's learning algorithm will be extended to include additional techniques such as constructive induction and rule utility analysis. Second, SCOPE will be more thoroughly tested; several real-world planning domains have been identified as possible testbeds, and more in-depth comparisons will be drawn between SCOPE and other competing approaches. Third, SCOPE will be implemented in a different planning system in order to test its portability to other planning algorithms. This work should demonstrate that machine-learning techniques can be a powerful tool in the quest for tractable real-world planning.
Technical Report AI96-250, Department of Computer Sciences, University of Texas.