Planning in Answer Set Programming using Ordered Task Decomposition

In this paper we introduce a formalism for solving Hierarchical Task Network (HTN) Planning using Answer Set Programming (ASP). We consider the formulation of HTN planning as described in the SHOP planning system and define a systematic translation method from SHOP's representation of the planning problem into logic programs with negation. We show that our translation is sound and complete: answer sets of the logic program obtained by our translation correspond exactly to the solutions of the planning problem. We compare our method to (1) similar approaches based on non-HTN planning and (2) SHOP, a dedicated planning system. We show that our approach outperforms non-HTN methods and that its performance is better with ASP systems that allow for nonground programs than with ASP systems that require ground programs. Keywords: HTN planning, nonmonotonic reasoning, ASP systems, benchmarks