Semantics for Hierarchical Task Network Planning

One big obstacle to understanding the nature of hierarchical task net work htn planning has been the lack of a clear theoretical framework In particular no one has yet presented a clear and concise htn algorithm that is sound and complete In this paper we present a formal syntax and se mantics for htn planning Based on this syntax and semantics we are able to de ne an algorithm for htn planning and prove it sound and complete We also develop several de nitions of expressivity for planning languages and prove that htn planning is strictly more expressive than strips style planning according to those de nitions