There are several advantages to the planning style that PbR introduces. First, PbR is a declarative domain-independent framework. This facilitates the specification of planning domains, their evolution, and the principled extension of the planner with new capabilities. Moreover, the declarative rewriting rule language provides a natural and convenient mechanism to specify complex plan transformations.
Second, PbR accepts sophisticated quality measures because it operates on complete plans. Most previous planning approaches either have not addressed quality issues or have very simple quality measures, such as the number of steps in the plan, because only partial plans are available during the planning process. In general, a partial plan cannot offer enough information to evaluate a complex cost metric and/or guide the planning search effectively.
Third, PbR can use local search methods that have been remarkably successful in scaling to large problems .3 By using local search techniques, high-quality plans can be efficiently generated. Fourth, the search occurs in the space of solution plans, which is generally much smaller than the space of partial plans explored by planners based on refinement search.
Fifth, our framework yields an anytime planning algorithm . The planner always has a solution to offer at any point in its computation (modulo the initial plan generation that needs to be fast). This is a clear advantage over traditional planning approaches, which must run to completion before producing a solution. Thus, our system allows the possibility of trading off planning effort and plan quality. For example, in query planning the quality of a plan is its execution time and it may not make sense to keep planning if the cost of the current plan is small enough, even if a cheaper one could be found. Further discussion and concrete examples of these advantages are given throughout the following sections.