Reasoning About Synchronic Groups

Swarm is a computational model which extends the UNITY model in three important ways: (1) UNITY’s fixed set of variables is replaced by an unbounded set of tuples which are addressed by content rather than by name; (2) UNITY’s static set of statements is replaced by a dynamic set of transactions; and (3) UNITY’s static ‖-composition is augmented by dynamic coupling of transactions into synchronic groups. This last feature, unique to Swarm, facilitates formal specification of the mode of execution (synchronous or asynchronous) associated with portions of a concurrent program and enables computations to restructure themselves so as to accommodate the nature of the data being processed and to respond to changes in processing objectives. This paper overviews the Swarm model, introduces the synchronic group concept, and illustrates its use in the expression of dynamically structured programs. A UNITY-style programming logic is given for Swarm, the first axiomatic proof system for a shared dataspace language.