  I describe a planning methodology for domains with uncertainty in the form of
external events that are not completely predictable. The events are represented
by enabling conditions and probabilities of occurrence. The planner is
goal-directed and backward chaining, but the subgoals are suggested by
analyzing the probability of success of the partial plan rather than being
simply the open conditions of the operators in the plan. The partial plan is
represented as a Bayesian belief net to compute its probability of success.
Since calculating the probability of success of a plan can be very expensive I
introduce two other techniques for computing it, one that uses Monte Carlo
simulation to estimate it and one based on a Markov chain representation that
uses knowledge about the dependencies between the predicates describing the
domain.
