Some Orders Are Important: Partially Preserving Orders in Top-Quality Planning

TL;DR

This paper introduces a flexible approach to top-quality planning that allows specifying important action orders, bridging the gap between fully ordered and unordered plans, and demonstrates the effectiveness of adapted search techniques.

Contribution

It proposes a novel framework for partially preserving action orders in top-quality planning and adapts partial order reduction techniques for this purpose.

Findings

Partial order reduction improves planning efficiency.

Flexible order preservation enhances plan quality.

Experimental results show computational benefits.

Abstract

The ability to generate multiple plans is central to using planning in real-life applications. Top-quality planners generate sets of such top-cost plans, allowing flexibility in determining equivalent ones. In terms of the order between actions in a plan, the literature only considers two extremes -- either all orders are important, making each plan unique, or all orders are unimportant, treating two plans differing only in the order of actions as equivalent. To allow flexibility in selecting important orders, we propose specifying a subset of actions the orders between which are important, interpolating between the top-quality and unordered top-quality planning problems. We explore the ways of adapting partial order reduction search pruning techniques to address this new computational problem and present experimental evaluations demonstrating the benefits of exploiting such techniques in this setting.