Charles L. Ortiz, Jr.
Most real-world planning problems arise in incompletely specified situations. One rather computationally expensive way to cope with such incompleteness is to formulate comprehensive contingency plans. A more attractive alternative is to instead design more flexible planning systems: for example, it should be possible for a planner to incorporate reasonable default information when available; it should also be possible for a planner to postpone planning parts of a plan lacking sufficient information and begin execution, if it is more likely to later be in a position to complete those parts of the plan. Conventional planners, however, are not sufficiently flexible in these respects; indeed, most plan representations still assume a completely specified world. This paper presents an extension to HTN planning -- called open-ended planning- in which preferences to certain plan-execution behaviors can be expressed in order to achieve such flexibility.