HDDL: An Extension to PDDL for Expressing Hierarchical Planning Problems

Abstract

The research in hierarchical planning has made considerable progress in the last few years. Many recent systems do not rely on hand-tailored advice anymore to find solutions, but are supposed to be domain-independent systems that come with sophisticated solving techniques. In principle, this development would make the comparison between systems easier (because the domains are not tailored to a single system anymore) and – much more important – also the integration into other systems, because the modeling process is less tedious (due to the lack of advice) and there is no (or less) commitment to a certain planning system the model is created for. However, these advantages are destroyed by the lack of a common input language and feature set supported by the different systems. In this paper, we propose an extension to PDDL, the description language used in non-hierarchical planning, to the needs of hierarchical planning systems.

Lilotane: A Lifted SAT-based Approach to Hierarchical Planning

“…Our planner accepts planning problems in the form of HDDL (Hierarchical Domain Description Language) files. HDDL has been proposed recently to consolidate a common input language for hierarchical planning (Höller, Behnke, Bercher, Biundo, Fiorino, Pellier, & Alford, 2020) and was used for the IPC 2020 (Behnke et al, 2020b).…”

“…The IPC was based on an exceptionally large and diverse set of benchmarks for hierarchical planning: In previous work the co-existence of various input formats of HTN planners hindered direct performance comparisons (e.g., Nau et al, 1999;Schreiber et al, 2019b;Höller et al, 2020), but for the IPC a de-facto standard format for hierarchical planning problems was established and many domain authors contributed a large variety of benchmarks. Table 3 lists averaged properties of old and new benchmarks in accordance with our complexity model.…”

The PANDA Framework for Hierarchical Planning

“…At the left of Fig. 1, two basic functionalities are given that are used by many other components: The standard input language HDDL [30] and our grounding procedure that integrates a reachability analysis [12].…”

“…For users wanting to integrate Problem Definition (Sec. 3.1) • HDDL definition [30] Preprocessing (Sec. 3.1)…”

“…In classical planning there is such a language, called Planning Domain Definition Language (PDDL) [25]. We developed the Hierarchical Domain Definition Language (HDDL), an extension to PDDL to support the definition of hierarchical planning problems, and proposed it as common input language [30]. It is the official input language for the International Planning Competition (IPC) 2020.…”