Revealing Hidden Preconditions and Effects of Compound HTN Planning Tasks – A Complexity Analysis

Abstract

In Hierarchical Task Network (HTN) planning, compound tasks need to be refined into executable (primitive) action sequences. In contrast to their primitive counterparts, compound tasks do not specify preconditions or effects. Thus, their implications on the states in which they are applied are not explicitly known: they are "hidden" in and depending on the decomposition structure. We formalize several kinds of preconditions and effects that can be inferred for compound tasks in totally ordered HTN domains. As relevant special case we introduce a problem relaxation which admits reasoning about preconditions and effects in polynomial time. We provide procedures for doing so, thereby extending previous work, which could only deal with acyclic models. We prove our procedures to be correct and complete for any totally ordered input domain. These results are embedded into an encompassing complexity analysis of the inference of preconditions and effects of compound tasks, an investigation that has not been made so far.

Hierarchical planning and reasoning about partially ordered plans—From theory to practice

“…(preconditions were defined similarly.) The results turned out to be the same as for landmarks: Determining whether a fact is precondition or an effect is as hard as solving the respective planning problem itself (Olz, Biundo, and Bercher 2021). However, we also identified a problem relaxation that allows computing some of these preconditions and effects in polynomial time.…”

“…Somehow related to the concept of landmarks is some of our more recent work on preconditions and effects of compound tasks (Olz, Biundo, and Bercher 2021). Recall that the purpose of compound tasks is just to get replaced by the plan of the chosen decomposition method.…”

Evolvable SPL management with partial knowledge

“…Yet, other complementary avenues still need to be explored to identify the relationships between solution components and source datasets. We are currently working on extracting the preconditions and effects of the algorithms by analyzing different techniques and ML environments [6,35,38,52]. Quality assurance.…”

Can They Come Together? A Computational Complexity Analysis of Conjunctive Possible Effects of Compound HTN Planning Tasks

“…This is also the case in HDDL , the official domain modeling language of the last and upcoming International Planning Competition (IPC). Olz, Biundo, and Bercher (2021), however, introduced inferred preconditions and effects of compound tasks based on their possible refinements in totalorder (t.o.) HTN planning in order to make their potential state transitioning visible.…”

“…Lastly, they provide additional information that can be exploited by heuristics and planners (Nau et al 2003;Waisbrot, Kuter, and Könik 2008;de Silva, Sardina, and Padgham 2009;Bit-Monnot, Smith, and Do 2016;Goldman and Kuter 2019;Magnaguagno, Meneguzzi, and de Silva 2021;Schreiber 2021). Olz, Biundo, and Bercher (2021) defined two types of effects. First, guaranteed effects, which are facts that are added or deleted by every executable refinement of a compound task, respectively.…”