Planning using Transformation between Equivalent Formalisms: A Case Study of Efficiency

Abstract

We have considered two planning formalisms which are known to be expressively equivalent---the CPS formalism, using propositional atoms, and the SAS + formalism, using multi-valued state variables. As a case study, we have modified a well-known partial-order planner for CPS into an `identical' planner for SAS + and we have considered two encodings of SAS + into CPS. It turns out that it is more efficient to solve SAS + instances by using the SAS + planner directly than to first encode them as CPS instances and use the CPS planner. For one encoding of SAS + into CPS, which is a polynomial reduction, the CPS planner has a polynomially or exponentially larger search space, depending on goal selection strategy. For the other encoding, which is not a polynomial reduction, the CPS search is of the same size as the SAS + search space, but the cost per node can be exponentially higher in this case. On the other hand, solving CPS instances by encoding them as SAS + instances and..