A model approximation scheme for planning in partially observable stochastic domains

Partially observable Markov decision processes (POMDPs) are a natural model for planning problems where e ects of actions are nondeterministic and the state of the world is not completely observable. It is di cult to solve POMDPs exactly. This paper proposes a new approximation scheme. The basic idea is to transform a POMDP into another one where additional information is provided by an oracle. The oracle informs the planning agent that the current state of the world is in a certain region. The transformed POMDP is consequently said to be region observable. It is easier to solve than the original POMDP. We propose to solve the transformed POMDP and use its optimal policy to construct an approximate policy for the original POMDP. Bycontrolling the amount of additional information that the oracle provides, it is possible to nd a proper tradeo between computational time and approximation quality. In terms of algorithmic contributions, we study in details how to exploit region observability insolving the transformed POMDP. To facilitate the study, we also propose a new exact algorithm for general POMDPs. The algorithm is conceptually simple and yet is signi cantly more e cient than all previous exact algorithms. 1