will clinger [1981] developed the first denotational actor model for concurrent computation that embodied unbounded nondeterminism. bill kornfeld and carl hewitt [1981] showed that the actor model could encompass large-scale concurrency. agha developed actors as a fundamental model for concurrent computation. his work on representing actor abstraction and composition, and on developing an operational semantics for actors based on asynchronous communications trees was explicitly influenced by milner's work on the calculus of communicating systems (ccs). as well the work of clinger.