Guarded Transitions in Evolving Specifications

  • Authors:
  • Dusko Pavlovic;Douglas R. Smith

  • Affiliations:
  • -;-

  • Venue:
  • AMAST '02 Proceedings of the 9th International Conference on Algebraic Methodology and Software Technology
  • Year:
  • 2002

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Abstract

We represent state machines in the category of specifications, where assignment statements correspond exactly to interpretations between theories [7, 8]. However, the guards on an assignment require a special construction. In this paper we raise guards to the same level as assignments by treating each as a distinct category over a shared set of objects. A guarded assignment is represented as a pair of arrows, a guard arrow and an assignment arrow. We give a general construction for combining arrows over a factorization system, and show its specialization to the category of specifications. This construction allows us to define the fine structure of state machine morphisms with respect to guards. Guards define the flow of control in a computation, and how they may be translated under refinement is central to the formal treatment of safety, liveness, concurrency, and determinism.