A Structural Complexity Analysis of Hierarchical Task Network Planning

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Cornelius Brand, Robert Ganian, Fionn Mc Inerney, Simon Wietheger

Published: 2025, Last Modified: 05 May 2026IJCAI 2025EveryoneRevisionsBibTeXCC BY-SA 4.0
Abstract: We perform a refined complexity-theoretic analysis of three classical problems in the context of Hierarchical Task Network Planning: the verification of a provided plan, whether an executable plan exists, and whether a given state can be reached. Our focus lies on identifying structural properties which yield tractability. We obtain new polynomial algorithms for all three problems on a natural class of primitive networks, along with corresponding lower bounds. We also obtain an algorithmic meta-theorem for lifting polynomial-time solvability from primitive to general task networks, and prove that its preconditions are tight. Finally, we analyze the parameterized complexity of the three problems.