Methodology : The Rational Statemate Approach : Two Aspects of System Description

Two Aspects of System Description

The graphical language of Rational Statemate provides a stationary description of what the system does (Activity-chart) and a dynamic description of when and how it does it (Statecharts).

The Activity-chart is the most important view in communicating what the system does. Activity-charts capture the functional view of the system by mapping system functions directly to activities. Hence the Activity-chart provides the static view of the main functions of the system. From the Activity-chart, the reader must be able to understand what the system does.

Although the Rational Statemate specification is entered into a computer, the final reader is still a person. Since the goal is to communicate the specification to people, it is important to keep in mind who the readers are. For control and hardware engineers, the Activity-chart is equivalent to a Block Diagram.

The Statechart provides a behavioral view or a dynamic description of the system. The Statechart can either describe the behavior of a single activity or control the overall execution of a number of activities.

A Statechart used only for controlling when processes are activated, suspended, or stopped is known as a control activity. This means the primary role of the Statechart used as a control activity is to start and stop the activities in the Activity-chart. This has a very natural mapping for our intended readers—Software engineers.

To Software engineers, Activity-charts graphically represent the subroutines they are familiar with as they show: hierarchy, input data, and output data. The control activity is the program main, which controls when subroutines are called. Thus the system should be structured in functional modules that make the specification more readable and later help in code generation.