CONCURRENCY AND ATOMICITY

We investigate the ability to regard a finite computation as a single event, in dealing with the semantics of concurrency. We propose a calculus of concurrent processes that embodies this ability in two respects: the first one is that of execution, the second that of operation. As usual, we formalize the execution of a process as a labeled transition relation, but at each step the action peformed is a compound one, namely, a labeled poset, not just an atom. Next we introduce a second transition relation, formalizing the operation of a process on data. As in the usual semantics of sequential programs, a process operates on data by means of its terminated sequences of computations. Then we obtain atomic actions by abstracting the whole operation of a process as a single event. We show that this abstraction mechanism allows us to deal with a variety of synchronization and communication disciplines.