Exploiting Symmetry in the Planning graph via Explanation-Guided Search

We present a method for exploiting the symmetry in the planning graph structure and certain redundancies inherent in the Graphplan algonthm, so as to improve its backward search. The main insight underlying our method is that due to these features the backward search conducted at level k + 1 of the graph is essentially a replay of the search conducted at the previous level k with certam well-defined extensions. Our method consists of maintaining a pilot explanation structure capturing the failures encountered at previous levels of the search, and using it in an intelligent way to guide the search at the newer levels. The standard EBL and DDB techniques can be employed to control the size of the pilot explanation. The technique has been implemented in the EGBG system, and we present a preliminary empirical study.

[1]  Subbarao Kambhampati,et al.  Understanding and Extending Graphplan , 1997, ECP.

[2]  Thomas Schiex,et al.  Solution Reuse in Dynamic Constraint Satisfaction Problems , 1994, AAAI.

[3]  Bernhard Nebel,et al.  Extending Planning Graphs to an ADL Subset , 1997, ECP.

[4]  Avrim Blum,et al.  Fast Planning Through Planning Graph Analysis , 1995, IJCAI.

[5]  Thomas Schiex,et al.  Nogood Recording for Static and Dynamic Constraint Satisfaction Problems , 1994, Int. J. Artif. Intell. Tools.

[6]  R. Dechter.  to Constraint Satisfaction , 1991 .

[7]  Rina Dechter,et al.  In Search of the Best Constraint Satisfaction Search , 1994, AAAI.

[8]  Subbarao Kambhampati,et al.  Improving Graphplan's Search with EBL & DDB Techniques , 1999, IJCAI.

[9]  Subbarao Kambhampati,et al.  On the Relations Between Intelligent Backtracking and Failure-Driven Explanation-Based Learning in Constraint Satisfaction and Planning , 1998, Artif. Intell..

[10]  Frank P. Coyle,et al.  Aaai '90 , 1990, IEEE Expert.

[11]  Manuela M. Veloso,et al.  Flexible Strategy Learning: Analogical Replay of Problem Solving Episodes , 1994, AAAI.

[12]  Subbarao Kambhampati,et al.  Storing and Indexing Plan Derivations through Explanation-based Analysis of Retrieval Failures , 1997, J. Artif. Intell. Res..

[13]  Thomas Schiex,et al.  Nogood Recording for static and dynamic constraint satisfaction problems , 1993, Proceedings of 1993 IEEE Conference on Tools with Al (TAI-93).

[14]  Patrick Prosser,et al.  Domain Filtering can Degrade Intelligent Backtracking Search , 1993, IJCAI.

[15]  Alan K. Mackworth.  Constraint Satisfaction , 1985 .

[16]  Brian Falkenhainer,et al.  Dynamic Constraint Satisfaction Problems , 1990, AAAI.