# HDDL 2.1: Towards Defining an HTN Formalism with Time

arXiv: https://arxiv.org/abs/2206.01822 · HTML: https://mlsanity.com/paper/2206.01822/

## Key facts

- Cited by 2 papers in the map (data through 14 Oct 2026).
- Builds on 1 of its 53 references that are in the map.
- First posted on arXiv 3 Jun 2022.

## Builds on (most cited first, 1 of 1)

- [Hierarchical Planning in the IPC](https://mlsanity.com/paper/1909.04405/) (2019)

## Built on by (most cited first, 2 of 2)

- [On Guiding Search in HTN Temporal Planning with non Temporal Heuristics](https://mlsanity.com/paper/2306.07638/) (2023)
- [Temporal Planning via Interval Logic Satisfiability for Autonomous Systems](https://mlsanity.com/paper/2406.09661/) (2024)

## Abstract (arXiv)

Real world applications of planning, like in industry and robotics, require modelling rich and diverse scenarios. Their resolution usually requires coordinated and concurrent action executions. In several cases, such planning problems are naturally decomposed in a hierarchical way and expressed by a Hierarchical Task Network (HTN) formalism. The PDDL language used to specify planning domains has evolved to cover the different planning paradigms. However, formulating real and complex scenarios where numerical and temporal constraints concur in defining a solution is still a challenge. Our proposition aims at filling the gap between existing planning languages and operational needs. To do so, we propose to extend HDDL taking inspiration from PDDL 2.1 and ANML to express temporal and numerical expressions. This paper opens discussions on the semantics and the syntax needed to extend HDDL, and illustrate these needs with the modelling of an Earth Observing Satellite planning problem.