UML State Machines
Jiacun Wang · 2017
This chapter focuses on state machine diagrams. A state machine diagram has four types of elements, namely states, transitions, events, and actions. States represent the possible operational modes of an object. Transitions represent legal changes from one state to another. Events are the labels of a transition, defining under what conditions the transition occurs. Actions are the activities that take place within a state. The chapter introduces the fundamental concepts of Unified Modeling Language (UML) state machines, such as hierarchy, concurrency, and modularity of graphic representation, as well as various graphic elements. At the end of the chapter, the antilock braking system (ABS) is used as example to show the application of UML state machines in real-world embedded system behavior modeling. A state in a UML state machine is modeled using a circular rectangle with the state's name being represented either inside the rectangle or outside the rectangle using a name tab.