Four combinators for concurrency
Robin Milner · 1982
An algebraic calculus of asynchronous parallel computation, called CCS (Calculus of Communicating Systems), was developed in [HM,Mil 1]. CCS can express both the semantics of parallel programming languages and the behaviour of data structures (mailbox, random access memory, buffer) which serve as interfaces between independent agents. The primitive notion is 'handshake' communication. The emphasis is upon (i) synthesis from components and (ii) extensionality (meaning = observable behaviour), in contrast with Petri's Net theory which emphasizes causal independence.