Workshop on Hierarchical Planning (HPlan)

7th ICAPS Workshop on Hierarchical Planning (HPlan 2024)
Banff, Alberta, Canada
Monday, June 3, 2024 Room KC 305

Aim and Scope of the Workshop

The motivation for using hierarchical planning formalisms is manifold. It features explicit and predefined guidance of the plan generation process and allows to represent complex problem solving and behavior patterns. A further benefit is that hierarchical planning offers different abstraction levels when communicating with a human user or when planning cooperatively. The best-known formalism in the field is Hierarchical Task Network (HTN) planning. In addition, there are several other hierarchical planning formalisms, e.g., hybrid planning (incorporating aspects from POCL planning), Hierarchical Goal Network (HGN) planning (incorporating a hierarchy on goals), or formalisms that combine task hierarchies with timeline planning (e.g., ANML). Hierarchies induce fundamental differences from classical planning, creating distinct computational properties and requiring separate algorithms from non-hierarchical planners. Many of these aspects of hierarchical planning are still unexplored. Thus, we encourage any contribution, independent of the underlying hierarchical planning formalism, and want to provide a forum for researchers to discuss the various aspects of hierarchical planning.

Topics of Interest

Topics of interests include but are not limited to:

  • theoretical foundations, e.g., complexity results
  • heuristics, search, and other solving techniques for plan generation
  • techniques and foundations for providing modeling support
  • challenges and lessons learned from modeling systems (using hierarchical models)
  • applications of hierarchical planning
  • plan explanation for hierarchical models
  • hierarchical plan repair techniques
  • techniques for verifying solutions of hierarchical planning problems
  • techniques for automated learning and synthesis of hierarchical models

Important Dates

  • Submission Deadline: Monday, 25 March 2024 (AoE)
  • Author Notification: Friday, 26 April 2024
  • Camera-Ready Deadline: Friday 24 May 2024 (AoE)
  • Workshop: Monday, June 3, 2024

We understand that for some, our notification date might come too late in order to plan travel accordingly, in particular if visa needs to be obtained. So in case you want to make your travel plans dependent on paper acceptance and thus require an earlier notification, please reach out to us to see whether submission and notification dates can be moved forward for your individual paper.

Submission Details

The formatting guidelines (author kit, etc.) are the same as for ICAPS 2024. There will be a high quality double-blind review process against the standard criteria of significance, soundness, scholarship, clarity, and reproducibility. However, submissions may be less evolved than at the main conference. We have two categories:

We have two categories:

  1. Technical research papers (short or long) and
  2. Challenge papers (short).

Technical research papers correspond to standard conference papers, but may be less evolved or groundbreaking. The purpose of challenge papers is to make aware of interesting/important problems in Hierarchical Planning and to encourage discussion at the workshop – not to present some significant contribution.

Authors may submit long papers (up to 8 pages plus up to one page of references) or short papers (up to 4 pages plus up to one page of references). The purpose of short papers is to encourage publications of more preliminary results; challenge papers need to be short papers.

In case of acceptance, the full 9, resp. 5, pages can be used for the paper.

Submissions will be done via easychair.

As written above, we are happy to check whether we can arrange an earlier submission, review, and notification date to accommodate your travel plans if required (e.g., for Visa). In this case we have to see how submissions will be done. Either way, contact the organizers at your earliest convenience in case you require this.

Workshop Proceedings

On top of making all papers available for download individually, we also collect them in a single proceedings that we will also make publicly available (check out previous years’ editions if interested: hplan.hierarchical-task.net).

Our proceedings are non-archival meaning that authors keep all copyrights.

Policy on Previously Published Material

If you are interested in presenting work on hierarchical planning that was accepted or published at some other conference or journal (to promote your work to the hierarchical planning community), please contact the organizers. We will not include such a paper into our proceedings, but we are happy to discuss options for presenting such work.

Despite our proceedings being non-archival we will strictly not include any paper where at the time of putting the proceedings online, portions of that paper are under the copyright of some publisher. The reason is that normally the rights granted to the authors are rather restricted; they might be allowed to upload the specific entire paper on their own institution’s webpage, but this does not include allowing others (like us workshop organizers) to distribute that material or parts of it. This means that all submitted work must be entirely original – just as at any conference. If in doubt, contact the organizers.

We do allow and also explicitly encourage the submission of papers that at the time of submission are under review at another conference. Note that other conferences usually allow material that is under review at a workshop in parallel, but do not allow papers currently being under review at another archival conference or journal (HPlan is non-archival). If however the paper is also accepted at the respective conference, it will not be included in our proceedings to prevent any possible copyright infringements. Note that even for ECAI (which does not take copyrights as papers are put under a creative commons license) we will not include the paper in our proceedings. We will still mention the paper as being accepted at the workshop and expect the paper be part of the program (and thus presented like all other papers), but no final paper can be submitted for our workshop/proceedings. Instead, the proceedings will include links to the respective conference paper version. Please check out websites and proceedings of the previous years (hplan.hierarchical-task.net) to see examples of how this is done.

Invited Talk

Daniel Höller

Daniel Höller has been a post-doctoral researcher in Jörg Hoffmann's Foundations of AI Group at Saarland University since 2020. Before that, he was at the Institute of Artificial Intelligence at Ulm University, where he did this PhD on hierarchical planning (mainly HTN planning), supervised by Susanne Biundo. His PhD thesis on hierarchical planning won the ICAPS Best Dissertation Award in 2024. Besides HTN planning, his work is concerned with lifted planning, and with the combination of machine learning and planning.

He is interested in many aspects of HTN planning like the expressivity of different formalisms, translations of related problems like plan and goal recognition and plan verification, and especially solving techniques. He has worked on grounding, heuristic plan space and progression search, translations to classical planning, and to propositional logic. He is a main developer of the planning systems PANDA, TOAD, and LiSAT. At the 2023 International Planning Competition, the winners of all 6 tracks on HTN planning have been based on PANDA, as well as 5 out of 6 runner-ups.

HTN Planning as Heuristic Progression Search in the PANDA Framework

PANDA is a framework to solve different tasks around hierarchical planning. It comes with components for pre-processing, solving planning problems, and techniques for related tasks like plan and goal recognition, plan repair, and plan verification. It includes several solvers for hierarchical planning problems, namely heuristic plan space search, compilations to propositional logic, BDDs, and classical (i.e., non-hierarchical) planning, and heuristic progression (i.e., forward) search. In this talk, I will first give an overview of the different parts of PANDA. Then, we will have a detailed look at the forward progression search system: its pre-processing, search algorithm, and heuristics.

Workshop Committee

Organizing Committee

  • Pascal Bercher, pascal.bercher at anu.edu.au, webpage
  • Dominik Schreiber, dominik.schreiber at kit.edu, webpage
  • Simona Ondrčková, ondrckova at ktiml.mff.cuni.cz
  • Ron Alford, ronwalf at volus.net, webpage

Program Committee

If you’d like to be part of our team this year or in any of the future years, please reach out to the organizers!

  • Ron Alford, The MITRE Corporation
  • Gregor Behnke, University of Amsterdam
  • Pascal Bercher, The Australian National University
  • Maurice Dekker, University of Amsterdam
  • Humbert Fiorino, Université Grenoble Alpes
  • Christopher Geib, SIFT LLC
  • Daniel Höller, Saarland University, Saarland Informatics Campus
  • Prakash Jamakatel, University of Bundeswehr München
  • Jane Jean Kiam, Universität der Bundeswehr München
  • Pascal Lauer, Saarland University
  • Songtuan Lin, The Australian National University
  • Simona Ondrčková, Charles University
  • Kristýna Pantůčková, Charles University
  • Mark Roberts, The US Naval Research Laboratory
  • Enrico Scala, University of Brescia
  • Dominik Schreiber, Karlsruhe Institute of Technology
  • Mohammad Yousefi, The Australian National University

List of Accepted Papers

Accepted at HPlan and included in proceedings

The following publications will be included in the proceedings once they are ready.


Accepted at HPlan and another venue

The following publications will be excluded from the proceedings to prevent copyright issues. We will provide a link instead.


Presentations of papers from other venues

The following previously published papers are presented in the program but were not submitted to HPlan. (See “Policy on Previously Published Material”, where we offer to give you a forum to present work that was accepted at another venue already.)


Workshop Schedule

Our workshop is scheduled for Monday, June 3, 2024. It takes place in room KC 305.

UPDATE! We moved the invited talk to the afternoon session! This is our (still) preliminary schedule:

  •   8:30 –   8:40       Welcome
  •   8:40 –   9:00       poster teaser talks for session 1 (5 talks)
  •   9:00 – 10:00       poster session 1 (5 posters)
  • 10:00 – 10:30       BREAK
  • 10:30 – 10:50       poster teaser talks for session 2 (6 talks)
  • 10:50 – 12:00       poster session 2 (6 posters)
  • 12:00 – 13:30       BREAK
  • 13:30 – 14:30       Invited talk (including discussion)
  • 14:30 – 15:00       A discussion on an novel HTN formalism in the presence of empty decomposition methods, by Roman Barták (~10 min talk + open discussion)

Poster session 1:

  • An ILP Heuristic for Total-Order HTN Planning
  • On Semantics of Hierarchical Planning Domain Models with Decomposition Constraints and Empty Methods
    (This previously accepted paper will only be presented in a short talk and discussion at the end)
  • moved: Correcting Totally-Ordered Hierarchical Plans by Action Deletion and Action Insertion
  • Laying the Foundations for Solving FOND HTN problems: Grounding, Search, Heuristics (and Benchmark Problems)
  • Redundant Decompositions in PO HTN Domains: Goto Considered Harmful
  • Towards Search Node-Specific Special-Case Heuristics for HTN Planning – An Empirical Analysis of Search Space Properties under Progression

Poster Session 2:

  • A Comparative Analysis of Plan Repair in HTN Planning
  • Barely Decidable Fragments of HTN Planning
  • Correcting Totally-Ordered Hierarchical Plans by Action Deletion and Action Insertion
    (This poster is moved to the first session!)
  • HTN Model repair by completing incomplete methods (not an HPlan paper)
  • Toward Planning with Hierarchical Decompositions and Time-frames
  • Weighted Randomized Anytime Planning in Pyhop

Please note that we expect that all posters will be available during both sessions (though isn’t confirmed yet), but we only expect presenters to be available in those sessions in which the respective teaser talks were presented. Also note that we will present the list of which papers get presented in which session in time.

Further Information

  • On the HPlan website hplan.hierarchical-task.net you find, among others, a list of bibtex entries for all accepted papers in all HPlan editions. Individual workshop pages of past editions are available by adding the respective year, e.g., you may use hplan2023.hierarchical-task.net for last year’s edition (or 2024 for this very page).
  • We have a mailing list (via google groups) for hierarchical planning with currently approx. 70 subscribers. The list is almost zero traffic, moderated, and only allows mails related to hierarchical planning! Interested? Drop Pascal an email.