  This paper discusses the problem of abstracting conditional probabilistic
actions. We identify two distinct types of abstraction: intra-action
abstraction and inter-action abstraction. We define what it means for the
abstraction of an action to be correct and then derive two methods of
intra-action abstraction and two methods of inter-action abstraction which are
correct according to this criterion. We illustrate the developed techniques by
applying them to actions described with the temporal action representation used
in the DRIPS decision-theoretic planner and we describe how the planner uses
abstraction to reduce the complexity of planning.
