Using temporal logics to express search control knowledge for planning

Over the years increasingly sophisticated planning algorithms have been developed. These have made for more efficient planners, but unfortunately these planners still suffer from combinatorial complexity even in simple domains. Theoretical results demonstrate that planning is in the worst case intractable. Nevertheless, planning in particular domains can often be made tractable by utilizing additional domain structure. In fact, it has long been acknowledged that domain-independent planners need domain-dependent information to help them plan effectively. In this work we present an approach for representing and utilizing domain-specific control knowledge. In particular, we show how domain-dependent search control knowledge can be represented in a temporal logic, and then utilized to effectively control a forward-chaining planner. There are a number of advantages to our approach, including a declarative semantics for the search control knowledge; a high degree of modularity (new search control knowledge can be added without affecting previous control knowledge); and an independence of this knowledge from the details of the planning algorithm. We have implemented our ideas in the TLplan system, and have been able to demonstrate its remarkable effectiveness in a wide range of planning domains.