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8.1 Action States
As discussed in Chapter 2, as elements
communicate with one another within a society of
objects, each element has the responsibility of
appropriately reacting to the communications it receives. An
action state represents processing as an element
fulfills a responsibility. There are various types of action states,
including simple, initial, and final action states. The next few
sections discuss these different types of action states.
8.1.1 Simple Action States
A simple action state represents
processing. For example, the project
management system may have the following simple action states:
Project Manager Enters Report Criteria
Indicates that the project manager enters report criteria
Project Management System Generates Report
Indicates that the project management system generates a report
Printer Prints Report
Indicates that the printer prints the report
In the UML, an action state is shown as a shape with a straight top
and bottom and convex arcs on the two sides, and is labeled with the
name of an operation or a description of the processing. Figure 8-1 shows the various action states associated
with the project management system.
Figure 8-1. Simple action states
8.1.2 Initial and Final Action States
An initial action state indicates the
first action state on an activity diagram. In
the UML, an initial action state is shown using a small solid filled
circle. A final action state indicates the last
action state on an activity diagram. In the UML, a final action state
is shown using a circle surrounding a small solid filled circle (a
bull's eye). Figure 8-2 updates
Figure 8-1 with an initial and final action state.
An activity diagram may have only one initial action state,
but may have any number of final action states.
Figure 8-2. Simple, initial, and final action states
