Functional Strips: a More Flexible Language for Planning and Problem Solving

EEective planning requires good modeling languages and good algorithms. The Strips language has shaped most of the work in planning since the early 70's due to its eeective solution of the frame problem and its support for divide-and-conquer strategies. In recent years, however, planning strategies not based on divide-and-conquer and work on theories of actions suggest that alternative languages can make modeling and planning easier. With this goal in mind, we have developed Functional Strips, a language that adds rst-class function symbols to Strips providing additional exibility in the codiication of planning problems. This extension is orthogonal and complementary to extensions accommodated in other languages such as conditional eeects, quantiication, negation, etc. Function symbols, unlike relational symbols, can be nested so objects need not be referred to by their explicit names and as a result more eecient encodings can be provided. For example, a problem like the 8-puzzle can be codiied in terms of four actions with no arguments; Hanoi, can be codiied with a number of ground actions independent of the number of disks; resources and constraints can be easily represented, etc. Functional Strips is both an action and a planning language in the sense that actions are understood declaratively in terms of a state-based semantics and operationally in terms of eecient updates on state representations. In this paper, we present the language, the semantics and a number of examples, and discuss possible uses in planning and problem solving.