HDDL 2.1: Towards Defining a Formalism and a Semantics for Temporal HTN Planning

TL;DR

This paper proposes extending HDDL, a hierarchical planning language, to include temporal and numerical constraints inspired by PDDL 2.1, aiming to better support real-world applications requiring complex, coordinated actions.

Contribution

It introduces a formalism and semantic considerations for an extended HDDL 2.1 to incorporate temporal and numerical features for hierarchical planning.

Findings

Identifies the gap between HDDL and real-world planning needs.

Proposes a formal extension inspired by PDDL 2.1.

Discusses semantics and syntax for future HDDL 2.1 development.

Abstract

Real world applications as in industry and robotics need modelling rich and diverse automated planning problems. Their resolution usually requires coordinated and concurrent action execution. In several cases, these problems are naturally decomposed in a hierarchical way and expressed by a Hierarchical Task Network (HTN) formalism. HDDL, a hierarchical extension of the Planning Domain Definition Language (PDDL), unlike PDDL 2.1 does not allow to represent planning problems with numerical and temporal constraints, which are essential for real world applications. We propose to fill the gap between HDDL and these operational needs and to extend HDDL by taking inspiration from PDDL 2.1 in order to express numerical and temporal expressions. This paper opens discussions on the semantics and the syntax needed for a future HDDL 2.1 extension.