Exploiting Opportunities Using Planning Graphs

Opportunities arise in planning when changes in the environment make new propositions available to the planner. Replanning methods often focus only on the negative e ects that changes in the environment have and therefore do not apply well. This paper introduces a method that is speci cally focused on the opportunity problem. This method is based on the potential graph structure. This potential graph is basically an annotated version of the planning graph as used in many contemporary planners. We show how this potential graph can be used to discover the positive impact of opportunities. This information can then be used to improve upon the plan by exploiting such opportunities. The bene t of this method over standard planning techniques is two-fold: rstly, it can be used in an any-time algorithm. That is, when only little time is available, little improvements are quickly found. With more time available, greater improvements may be found. Secondly, this technique helps us focus on those parts of the plan that might be improved. Other parts are not changed, which greatly adds to the e ciency of the method. The applicability of the method is demonstrated by some initial experiments.