A Model of Contingent Planning for Agent Programming Languages

In this paper, we develop a formal model of planning for an agent that is operating in a dynamic and incompletely known environment. We assume that both the agent's task and the behavior of the agents in the environment are expressed as high-level nondeterministic concurrent programs in some agent programming language (APL). In this context, planning must produce a deterministic conditional plan for the agent that can be successfully executed against all possible executions of the environment program. We handle actions with nondeterministic effects, as well as sensing actions, by treating them as actions that trigger an environmental reaction that is not under the planning agent's control. Our model of contingent planning is specified for a generic APL with a transition semantics. Within this model, we devise a general procedure for computing the contingent plans. We also show how the model can be instantiated in the situation calculus with programs for the agent and the environment expressed in ConGolog, and we describe an implementation of the planning mechanism in this case.