A Faster Algorithm for Checking the Dynamic Controllability of Simple Temporal Networks with Uncertainty

Luke Hunsberger

Abstract

A Simple Temporal Network (STN) is a structure containing time-points and temporal constraints that an agent can use to manage its activities. A Simple Temporal Network with Uncertainty (STNU) augments an STN to include contingent links that can be used to represent actions with uncertain durations. The most important property of an STNU is whether it is dynamically controllable (DC)—that is, whether there exists a strategy for executing its time-points such that all constraints will necessarily be satisfied no matter how the contingent durations happen to turn out (within their known bounds). The fastest algorithm for checking the dynamic controllability of STNUs reported in the literature so far is the O(N4)-time algorithm due to Morris. This paper presents a new DC-checking algorithm that empirical results confirm is faster than Morris’ algorithm, in many cases showing an order of magnitude speed-up. The algorithm employs two novel techniques. First, new constraints generated by propagation are immediately incorporated into the network using a technique called rotating Dijkstra. Second, a heuristic that exploits the nesting structure of certain paths in the STNU graph is used to determine a good order in which to process the contingent links during constraint propagation.

References

  1. Chien, S., Sherwood, R., Rabideau, G., Zetocha, P., Wainwright, R., Klupar, P., Gaasbeck, J. V., Castano, R., Davies, A., Burl, M., Knight, R., Stough, T., and Roden, J. (2002). The techsat-21 autonomous space science agent. In The First International Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS-2002), pages 570-577. ACM Press.
  2. Cormen, T. H., Leiserson, C. E., Rivest, R. L., and Stein, C. (2009). Introduction to Algorithms. MIT Press.
  3. Dechter, R., Meiri, I., and Pearl, J. (1991). Temporal constraint networks. Artificial Intelligence, 49:61-95.
  4. Hunsberger, L. (2013a). A faster execution algorithm for dynamically controllable STNUs. In Proceedings of the 20th Symposium on Temporal Representation and Reasoning (TIME-2013).
  5. Hunsberger, L. (2013b). Magic loops in simple temporal networks with uncertainty. In Proceedings of the Fifth International Conference on Agents and Artificial Intelligence (ICAART-2013).
  6. Hunsberger, L., Posenato, R., and Combi, C. (2012). The dynamic controllability of conditional stns with uncertainty. In Proceedings of the PlanEx Workshop at ICAPS-2012, pages 121-128.
  7. Morris, P. (2006). A structural characterization of temporal dynamic controllability. In Principles and Practice of Constraint Programming (CP 2006), volume 4204 of Lecture Notes in Computer Science, pages 375-389. Springer.
  8. Morris, P., Muscettola, N., and Vidal, T. (2001). Dynamic control of plans with temporal uncertainty. In Nebel, B., editor, 17th International Joint Conference on Artificial Intelligence (IJCAI-01), pages 494-499. Morgan Kaufmann.
  9. Morris, P. H. and Muscettola, N. (2005). Temporal dynamic controllability revisited. In Veloso, M. M. and Kambhampati, S., editors, The 20th National Conference on Artificial Intelligence (AAAI-2005), pages 1193-1198. MIT Press.
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Paper Citation


in Harvard Style

Hunsberger L. (2014). A Faster Algorithm for Checking the Dynamic Controllability of Simple Temporal Networks with Uncertainty . In Proceedings of the 6th International Conference on Agents and Artificial Intelligence - Volume 1: ICAART, ISBN 978-989-758-015-4, pages 63-73. DOI: 10.5220/0004758100630073


in Bibtex Style

@conference{icaart14,
author={Luke Hunsberger},
title={A Faster Algorithm for Checking the Dynamic Controllability of Simple Temporal Networks with Uncertainty},
booktitle={Proceedings of the 6th International Conference on Agents and Artificial Intelligence - Volume 1: ICAART,},
year={2014},
pages={63-73},
publisher={SciTePress},
organization={INSTICC},
doi={10.5220/0004758100630073},
isbn={978-989-758-015-4},
}


in EndNote Style

TY - CONF
JO - Proceedings of the 6th International Conference on Agents and Artificial Intelligence - Volume 1: ICAART,
TI - A Faster Algorithm for Checking the Dynamic Controllability of Simple Temporal Networks with Uncertainty
SN - 978-989-758-015-4
AU - Hunsberger L.
PY - 2014
SP - 63
EP - 73
DO - 10.5220/0004758100630073