We explore the interactions between programvariable state visibility and communication behaviour in state-rich CSP-like processes, using the Unifying Theories of Programming (UTP) framework. The key results of this work are: having variable state visible while a process is waiting to communicate, results in an operationally complex theory of behaviour; by contrast, considering state as unobservable during communication waitperiods results in an elegant theory, with much cleaner operational intuitions. The language constructs most affected by this observability choice are those of external choice and parallel composition. We also discuss situations where this state hiding can prevent the adoption of interesting operators that seize control from waiting processes.
Abstract. This paper describes a complete denotational semantics, in the UTP framework, of slotted-Circus, a generic framework for reasoning about discrete timed/synchronously clocked systems. The key result presented here is a comprehensive semantics of the entire language that addresses various semantics issues that have been uncovered, whilst laying foundations for future extensions, particularly towards prioritized choice.
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