HDDL 2.1: Towards Defining an HTN Formalism with Time
This work addresses the gap in planning languages for industrial and robotics applications requiring hierarchical decomposition, but it is incremental as it builds on existing formalisms.
The authors tackled the challenge of modeling complex real-world planning scenarios with temporal and numerical constraints by proposing an extension to the HDDL language, inspired by PDDL 2.1 and ANML, and illustrated it with an Earth Observing Satellite problem.
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.