Action Systems: A Method Combining State-Based and Event-Based Specification

Abstract

Action systems [1] combine a definition of system state with an explicit description of how and when state-modifying events may occur. This example follows the work of Morgan [7] and Butler [2], in which these two aspects are given equal importance. Action systems describe both the succession of events in a system and the way in which system state changes. However, they are not tied to any one particular state-description notation and may be thought of as providing a framework which can, if required, be combined with other approaches. For example, the Z notation [10] offers significant advantages in the way state descriptions can be structured. This can be put to use within an action system as demonstrated below. The additional aspect of supporting event description and refinement means that features of event-based notations such as CSP [5] can be exploited for action systems too.