Explicit-state abstraction: a new method for generating heuristic functions

  • Authors:
  • Malte Helmert;Patrik Haslum;Jörg Hoffmann

  • Affiliations:
  • Albert-Ludwigs-Universität Freiburg, Freiburg, Germany;NICTA & Australian National University, Canberra, Australia;University of Innsbruck, STI, Innsbruck, Austria

  • Venue:
  • AAAI'08 Proceedings of the 23rd national conference on Artificial intelligence - Volume 3
  • Year:
  • 2008

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Abstract

Many AI problems can be recast as finding an optimal path in a discrete state space. An abstraction defines an admissible heuristic function as the distances in a smaller state space where arbitrary sets of states are "aggregated" into single states. A special case are pattern database (PDB) heuristics, which aggregate states if they agree on the state variables inside the pattern. Explicit-state abstraction is more flexible, explicitly aggregating selected pairs of states in a process that interleaves composition of abstractions with abstraction of the composites. The increased flexibility gains expressive power: sometimes, the real cost function can be represented concisely as an explicit-state abstraction, but not as a PDB. Explicit-state abstraction has been applied to planning and model checking, with highly promiSing empirical results.