Heuristic Search for Planning with Different Forced Goal-Ordering Constraints

Jiangfeng Luo,Weiming Zhang,Jincai Huang,Jing Cui,Zhong Liu,Cheng Zhu

doi:10.1155/2013/963874

Jiangfeng Luo, Weiming Zhang + Show 4 more

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https://doi.org/10.1155/2013/963874

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Abstract

Planning with forced goal-ordering (FGO) constraints has been proposed many times over the years, but there are still major difficulties in realizing these FGOs in plan generation. In certain planning domains, all the FGOs exist in the initial state. No matter which approach is adopted to achieve a subgoal, all the subgoals should be achieved in a given sequence from the initial state. Otherwise, the planning may arrive at a deadlock. For some other planning domains, there is no FGO in the initial state. However, FGO may occur during the planning process if certain subgoal is achieved by an inappropriate approach. This paper contributes to illustrate that it is the excludable constraints among the goal achievement operations (GAO) of different subgoals that introduce the FGOs into the planning problem, and planning with FGO is still a challenge for the heuristic search based planners. Then, a novel multistep forward search algorithm is proposed which can solve the planning problem with different FGOs efficiently.

Highlights

A large majority of real-world problems have interfering subgoals
As all the forced goal-ordering (FGO) exist in the initial state and are irrelevant to the approach for each atomic goal to be achieved, the search can arrive at the goal state if and only if all the atomic goals are achieved by a correct sequence
This paper evaluates the proposed algorithm Ex MsFS by comparing it with the following planning systems: (1) FF planning system [2], in which the Goal Agenda Manager (GAM) heuristic is used for the detection of goal ordering, (2) SGPlan6 [13], which adopts the incremental planning process to handle the goal orderings, (3) LAMA 2008 planning system [5], which adopts the hill-climbing strategy where the preferred actions of each step are selected by the FF and landmark heuristics

Summary

Introduction

A large majority of real-world problems have interfering subgoals. How to effectively plan for the interfering subgoals, especially when there are forced goal-ordering (FGO) constraints, has been a long term focus. As the Goal Agenda Manager (GAM) [1] used in the FF planner [2] and the ordered landmarks [3, 4] introduced in the LAMA planner [5], quite a number of approaches have been proposed but the performance results have scarcely improved. This is because, if any of the FGO constraints is violated, forward search may arrive at a deadlock, from which there is no way to reach the goal state. This paper proposes an approach that can automatically put right the planning process when it leads the search to a deadlock and significantly improve the planning efficiency

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Conclusion