Learning UML

Flow Transitions

Given a collection of action states, how are those action states related to one another? Flow transitions address this issue. As discussed in Chapter 2, a flow transition shows how action states are ordered or sequenced. There are various types of flow transitions, including control-flow and object-flow transitions, which are mentioned in Chapter 2 and discussed here.

Control-Flow Transitions

A control-flow transition indicates the order of action states. That is, once a source action state completes its processing, a target action state starts its processing. For example, the project management system may have the following order of action states for the task of generating a report:

1. The Project Manager Enters Report Criteria action state occurs first, because the project manager must enter the report criteria before the system can generate a report.

2. The Project Management System Generates Report action state occurs next, because the project management system must generate the report before the printer can print the report.

3. The Printer Prints Report action state occurs last, once the report has been generated by the project management system.

In the UML, a control-flow transition is shown as a solid line from a source action state to a target action state. Figure 8-3 shows the order of action states associated with the project management system.

Figure 8-3. Control-flow ...