Programs are complex Functions in a Server or underlying system that can be invoked and managed by a Client. Programs can represent any level of functionality within a system or process in which Client control or intervention is required and progress monitoring is desired. Figure 2 illustrates the model.

Figure 2 – Program illustration

Programs are stateful and transition through a prescribed sequence of states as they execute. Their behaviour is defined by a Program Finite State Machine (PFSM). The elements of the PFSM describe the phases of a Program’s execution in terms of valid transitions between a set of states, the stimuli or causes of those transitions, and the resultant effects of the transitions.