A²CCS: A Simple Extension of CCS for Handling Atomic Actions

The paper presents an operational model of atomic actions based on compositional transition systems. A notion of abstraction between lower level and higher level transition systems is defined, where actions, in the higher level correspond to sequences of actions in the lower level. Abstraction and composition are proved to commute. The approach is applied to an extended version of CCS, called A2CCS, where a prefix operation containing an underlined action symbol expresses the fact that the action, when executed, must be part of a sequence of actions performed in an atomic manner.