Undone Elena

[Queila Neubecker]

Prologhas been used as an inference engine of many systems, and it is natural to use Prolog as an inference engine of intelligent agent systems. However, Prolog assumes that a program does not change. This poses a problem because the agent might work in a dynamic environment where unexpected things can happen. In order to use a Prolog-like procedure as an inference engine of an agent, the procedure should be able to modify the computation, if necessary, after updating the program or executing an action. We introduce a new Prolog-like procedure which integrates planning, action execution, program updates, and plan modifications. Our new procedure computes plans by abduction. During or after a computation, it can update a program by adding a rule to the program or deleting a rule from the program. After updating the program, it modifies the computation, cuts invalid plans, and adds new valid plans. We use the technique of Dynamic SLDNF (DSLDNF) [1] [2] to modify computation after updating a program. It is also possible to execute an action during or after planning. We can use three types of actions: an action without a side effect; an action with a side effect which can be undone; an action with a side effect which cannot be undone. Following the result of action execution, the procedure modifies the computation: invalid plans are erased; some actions are undone; some redundant actions are erased. Even if a plan becomes invalid, it is possible to switch to another plan without loss of correctness. Based on the technique described above, we implemented an intelligent mobile network agent system, pi-coPlangent.

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