Partial Plans Completion with GRAPHPLAN

Completion of partial plans is a subtask for many planning techniques such as plan reusing, replanning and accomplishing complex user goals. The new generation of fast planners such as Graphplan, Satplan and others, is characterized by very efficent planning algorithms which exploit techniques of multiple plans representation. Unfortunately it is fairly difficult to give Graphplan a partial plan fragment to complete, because the internal plan network representation, only represents ordered by levels and complete plans. On the other hand it is very easy and straigthforward to provide an initial partial plan to complete to a planner like UCPOP, because its planning algorithm completes a partial initial plan in the internal representation. We present an original technique for using Graphplan in order to solve partial plan completion problems. The technique, called domain embedding, modifies the problem domain in order to induce only solutions which are completion of the given partial plan. The technique is planner independent, that is to say it is proved to be correct without regards to the internal implementation details of the given planner. The result has a general validity in order to combine the flexibility of Ucpop-like planners with the performance of Graphplan, and it can be trasferred to any other planner with minor modifications depending on the planning model and representation. Experiments show that partial plan completion with Graphplan outperforms Ucpop despite of the additional cost due to domain embedding thus resulting in a suitable technique for partial plan completion.