Multi-agent actions under uncertainty: situation calculus, discrete time, plans and policies

David Poole

To appear IJCAI-97 Workshop on Nonmonotonic Reasoning, Action and Change Nagoya, Japan, Aug 1997.


We are working on a logic to combine the advantages of first-order logic, but using Bayesian decision theory (or more generally game theory) as a basis for handing uncertainty. This forms a logic for multiple agents under uncertainty. These agents act asynchronously, can have their own goals, have noisy sensors, and imperfect effectors. Recently we have developed the independent choice logic that incorporates all of these features. In this paper we discuss two different representations of time within this framework: the situation calculus and what is essentially the event calculus. We show how they both can be used, and compare the different ontological commitments made by each. Uncertainty is handled in terms of a logic which allows for independent choices and a logic program that gives the consequences of the choices. There are probabilities over the choices by nature. As part of the consequences are a specification of the utility of (final) states. In the situation calculus, agents adopt programs and programs lead to situations in possible worlds (which correspond to the possible outcomes of complete histories); given a probability distribution over possible worlds, we can get the expected utility of a program. In the event calculus view, actions are propositions and agents adopt policies which are logic programs to imply what the agent will do based on what it observes. Again the expected value of a policy can be computed. The aim is to choose the plan or policy that maximizes the expected utility. This paper overviews both approaches, and explains why I think the event calculus is the most promising approach.

You can get the paper.

You can also see the Slides for the talk.

Last updated 23 April 97 - David Poole