HDDL 2.1: Towards Defining an HTN Formalism with Time

TL;DR

This paper proposes an extension to the HDDL planning language to better handle complex real-world scenarios involving temporal and numerical constraints, inspired by PDDL 2.1 and ANML, demonstrated through satellite planning.

Contribution

It introduces a formalism extension for HDDL to incorporate temporal and numerical expressions, addressing a gap in modeling complex planning problems.

Findings

Extended HDDL to include temporal and numerical constraints

Illustrated the approach with Earth Observing Satellite planning

Opened discussions on semantics and syntax for the extension

Abstract

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.