contents
previous
D. State diagrams
State diagrams can also be useful during analysis
as well as design activities.
Such diagrams are typically used to exhibit detailed behavior in objects in a manner
similar to the way that activity diagrams were used for use cases. In fact the two types
of diagrams share similar features. The "activity" boxes in activity diagrams are
replaced by boxes for "states". An object is considered to be in one of these states
at any given time.
Each state typically involves certain duties (activities).
Sometimes these are of sufficient complexity to warrant representing the state by
means of another state diagram. This can be drawn inside the original state.
A state box generally has a title and may also have a list
of duties following prefixes like do/, entry/ (duties to be performed
upon entering the state), exit (duties to be performed upon exit from the state).
Transitions arrows between states can be labeled with
guards (as in activity diagrams), as well as with labels of the form
event/action or just event or just
/action. Here "event" is something causing the transition
and "action" is something that happens as a result of the transition.
Most, but not all, of these features are illustrated in the next example.
next