Bisimulation on speed: a unified approach

  • Authors:
  • Gerald Lüttgen;Walter Vogler

  • Affiliations:
  • Department of Computer Science, University of York, York, UK;Institut für Informatik, Universität Augsburg, Augsburg, Germany

  • Venue:
  • FOSSACS'05 Proceedings of the 8th international conference on Foundations of Software Science and Computation Structures
  • Year:
  • 2005

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Abstract

Two process–algebraic approaches have been developed for comparing two bisimulation–equivalent processes with respect to speed: the one of Moller/Tofts equips actions with lower time bounds, while the one by Lüttgen/Vogler considers upper time bounds instead. This paper sheds new light on both approaches by testifying to their close relationship. We introduce a general, intuitive concept of “faster–than”, which is formalised by a notion of amortised faster–than preorder. When closing this preorder under all contexts, exactly the two faster–than preorders investigated by Moller/Tofts and Lüttgen/Vogler arise. For processes incorporating both lower and upper time bounds we also show that the largest precongruence contained in the amortised faster–than preorder is not a proper preorder but a timed bisimulation. In the light of this result we systematically investigate under which circumstances the amortised faster–than preorder degrades to an equivalence.