Abstract
In many cases several entities, such as commercial companies, need to work together towards the achievement of joint goals, while hiding certain private information. To collaborate effectively, some sort of plan is needed to coordinate the different entities. We address the problem of automatically generating such a coordination plan while preserving the agents’ privacy. Maintaining privacy is challenging when planning for multiple agents, especially when tight collaboration is needed and a global high-level view of the plan is required. In this work we present the Greedy Privacy-Preserving Planner (GPPP), a privacy preserving planning algorithm in which the agents collaboratively generate an abstract and approximate global coordination plan and then individually extend the global plan to executable plans. To guide GPPP, we propose two domain independent privacy preserving heuristics based on landmarks and pattern databases, which are classical heuristics for single agent search. These heuristics, called privacy-preserving landmarks and privacy preserving PDBs, are agnostic to the planning algorithm and can be used by other privacy-preserving planning algorithms. Empirically, we demonstrate on benchmark domains the benefits of using these heuristics and the advantage of GPPP over existing privacy preserving planners for the multi-agent STRIPS formalism.
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Notes
The exact details of this relaxed problem are more involved, and are explained later in the paper.
When computing the achievers of p, only actions that can be performed before obtaining p are considered. This is usually estimated using delete relaxation [39].
We also experimented with using the A* [23] algorithm to find optimal plans for the PDB. Experimentally, we did not observe a substantial difference between the performance of the two algorithms for solving these simple single fact problems.
In the results in the previous tables, the averages were over a subset of these instances, as other planning algorithm/heuristic configurations did not solve all problem instances under the time limit.
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Acknowledgments
We thank the reviewers for their useful comments. We also thank Antonin Komoda and Michal Stolba for their extensive help with running GPPP on the CoDMAP servers. This work was supported by ISF Grant 933/13, and by the Helmsley Charitable Trust through the Agricultural, Biological and Cognitive Robotics Center of Ben-Gurion University of the Negev.
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Parts of this paper appeared as [34].
Appendix: GPPP versus MAFS on CoDMAP instances
Appendix: GPPP versus MAFS on CoDMAP instances
In this appendix we present additional results to those presented in Sect. 8.3, on a different set of problems: the problem instances used in CoDMAP for the domains Satellite, Elevators, Rover, Zenotravel, and Logistics. The purpose of these results is to compare the performance of GPPP and MAFS using the landmark projection heuristic, PP-LM, and 3PDB.
Table 8 shows the coverage results, i.e, number of instances solved under 30 min. Here too, we see a clear advantage for GPPP over MAFS, and for PP-LM over the projection landmarks (LM-Proj). Note that there is no clear winner when comparing PP-LM and 3PDB, suggesting that a combination of the two would work well.
The next set of results compares the runtime and solution cost of the different configurations. To do so, we average only over the instances solved by all the compared configurations (GPPP/MAFS, LM-Proj/PP-LM/3PDB). Since MAFS with the projection LM is unable to solve many instances, we compared it only against MAFS with PP-LM, and provide separate results where we compare MAFS with PP-LM against the other configurations to allow an average over more instances.
Table 9 shows the average runtime over the instances solved by MAFS with the projection LM heuristic and by MAFS with PP-LM, showing a clear advantage for MAFS with PP-LM. Table 10 presents the average runtime of all configurations (except for MAFS with the projection LM heuristic), where the average is over all instances solved by all configurations. Here we observe a clear advantage to GPPP over MAFS, and to 3PDB over PP-LM.
Regarding solution cost, we observe only one clear trend, which is that the solution found by MAFS with the projection-based heuristic is poorer than that with PP-LM. We did not observe a clear trend regarding the solution cost when comparing the other configurations (Tables 11 and 12).
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Maliah, S., Shani, G. & Stern, R. Collaborative privacy preserving multi-agent planning. Auton Agent Multi-Agent Syst 31, 493–530 (2017). https://doi.org/10.1007/s10458-016-9333-9
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DOI: https://doi.org/10.1007/s10458-016-9333-9