ON INTERVAL-BASED TEMPORAL PLANNING - AN IQ-STRATEGY

Allen & Koomen's interval planner and Dean & McDermott's time map manager (TMM) offer different approaches to temporal database management in planning. In this paper we present a temporal planning system that integrates ideas from both methods, and at the same time develops several new ideas. In particular, we treat time points and intervals within a common structure, and adopt an alternative method for handling temporal constraints based on constraint logic programming. To provide a proper characterization of actions within an interval environment, we invoke the notion of noninterference conditions to handle action interaction and the qualification problem. To deal with the persistence problem, we adopt a spectrum of methods based on TMM's stretching and clipping rules. We show that our approach allows a temporally minimum specification for preconditions, which not only improves the clarity of the specification of an action, but perhaps also reduces the computational cost of constraint satisfaction. The formal aspects of our temporal approach are encapsulated in an interval temporal logic called IQ which is functionally more expressive than first order logic. The specification of our temporal reasoning is modelled in IQ-Prolog - a computation-oriented subsidiary language of IQ.