Department of Computer Science and Technology

Technical reports

CCS with environmental guards

Juanito Camilleri

August 1992, 19 pages

DOI: 10.48456/tr-264


This paper investigates an extension of Milner’s CCS with agents guarded by propositions on the environment. The agent g ≫ E, pronounced E in an environment of which g holds, depends on the set of actions the environment in ready to perform. This dependency is realised by an operational semantics in which transitions carry ready-sets (of the environment) as well as the normal action symbols from CCS. A notion of strong bisimulation is defined on guarded agents via this semantics. It is a congruence and satisfies new equational laws (including a new expansion law) whicyh are shown to be complete for finite guarded agents. The laws are conservative over agents of traditional CCS. The guarding operator ≫ provides a dynamic, local, and clean syntactic means of expressing the behaviour of an agent depending on circumstance; it is more expressive than the unless operator presented in [Cam91] and the priority choice operator presented in [Cam90] and [CaW91], and yields a much simpler expansion theorem.

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BibTeX record

  author =	 {Camilleri, Juanito},
  title = 	 {{CCS with environmental guards}},
  year = 	 1992,
  month = 	 aug,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  doi = 	 {10.48456/tr-264},
  number = 	 {UCAM-CL-TR-264}