state machine diagrams,
formerly called state chart diagrams in UML 1, depict the dynamic behavior of an
entity based on its response to events, showing how the entity reacts to various
events depending on the current state that it is in. Create a
UML state machine
diagram to explore the nature of a:
the complex behavior of a class, actor, subsystem, or component.
Figure 1. A UML state machine
Diagram for a seminar during enrollment.
Create A state machine When Behavior Differs Based on State. A Seminar
object is fairly complex, reacting to events such a enrolling a student
differently depending on its current state, as you see depicted in
A state is a stage in the behaviour pattern of an entity.States are represented by the values of the attributes of an entity.For example, inFigure 1
a seminar is in the Open
For Enrollment state when it has been flagged as open and there are
seats available to be filled.
State Names Should be Simple but Descriptive
Question "Black Hole" States. A black hole state is one that has transitions into it but
Question "Miracle" States. A miracle state is one that has transitions out of it but
none into it.
A transition is a progression from one state to another and
will be triggered by an event that is either internal or external to the entity
being modeled.For a class,
transitions are typically the result of the invocation of an operation that
causes an important change in state, although it is important to understand that
not all method invocations will result in transitions.An action is something, in the case of a class it is an operation, that
is invoked by/on the entity being modeled.
Name Software Actions Using Implementation Language Naming Conventions
Name Actor Actions Using Prose
Indicate Entry Actions Only When Applicable For All Entry Transitions
Indicate Exit Actions Only When Applicable For All Exit Transitions
Model Recursive Transitions Only When You Want to Exit and Re-Enter the
A guard is a condition that must be true in order to
traverse a transition.
Guards Should Not Overlap. The guards on similar transitions leaving a state must be
consistent with one another.For
example guards such as x <0, x = 0, and x > 0 are consistent whereas guard such
as x <= 0 and x >= 0 are not consistent because they overlap.
In Figure 2you see that there are two transitions from
Taught as the result of the student
dropped event, whereas there is only one in
Figure 3- the transitions are combined into a single one that leads to a junction
point (the filled in circle).