By the same authors

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Comparing degrees of non-determinism in expression evaluation

Research output: Contribution to journalArticlepeer-review

Published copy (DOI)


  • Ian J. Hayes
  • Alan Burns
  • Brijesh Dongol
  • Cliff B. Jones


Publication details

JournalComputer journal
DateE-pub ahead of print - 5 Feb 2013
DatePublished (current) - 1 Jun 2013
Issue number6
Number of pages15
Pages (from-to)741-755
Early online date5/02/13
Original languageEnglish


Expression evaluation in programming languages is normally assumed to be deterministic; however, if an expression involves variables that are being modified by the environment of the process during its evaluation, the result of the evaluation can be non-deterministic. Two common scenarios in which this occurs are concurrent programs within which processes share variables and real-time programs that interact to monitor and/or control their environment. In these contexts, although any particular evaluation of an expression gives a single result, there is a range of possible values that could be returned depending on the relative timing between modification of a variable by the environment and its access within the expression evaluation. To compare the semantics of non-deterministic expression evaluation, one can use the set of possible values the expression evaluation could return. This paper formalizes three approaches to non-deterministic expression evaluation, highlights their commonalities and differences, shows the relationships between the approaches and explores conditions under which they coincide. Modal operators representing that a predicate holds for all possible evaluations and for some possible evaluation are associated with each of the evaluation approaches, and the properties and relationships between these operators are investigated. Furthermore, a link is made to a new notation used in reasoning about interference.

    Research areas

  • concurrency, Non-deterministic expression evaluation, real-time programming, rely-guarantee, sampling logic

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