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Appendix A Small UML Guide

Figure A-21.  A simple state (State A) and a composite state (State B), with nested sub-states (State B1 and State B2)

Transitions

Transitions are basically distinguished between external and internal transitions.

External Transitions

An external transition usually leads to a change of state. Switching from one state to another is called state transition. However, it is also possible that the start and end state of an external transition are the same. The syntax (notation) of an external transition is a solid line with an open arrowhead, as depicted in Figure A-22.

Figure A-22.  External transitions

Internal Transitions

Sometimes an event causes some internal behavior to execute but does not lead to a state change. This is called an internal transition. Internal transitions are noted within a state’s compartment, as depicted in Figure A-23.

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