Information Technology Reference
In-Depth Information
make it up. For the creation of a state diagram to be possible, the system must have
a finite number of states, or an abstraction must be used to this end. State transition
diagrams, similarly, depict all of the information involved in a state change,
including the events that trigger the change and the actions that occur as a result of
it. Harel provided the following common notations for use in state diagrams
(Figs.
3.14
,
3.15
,
3.16
).
The first image is used to depict a state, which is given a unique name and, if
necessary, some actions that are associated with it. The second shows a history
icon, which can be attached to a state to indicate its' lastly assumed state, which it
will go into upon entry. The last image depicts state nesting, in which a superstate
consists of some number of substates.
Actions are often associated with states in the sense that they occur when a state
changes (i.e.: when a state is entered or exited). State transitions connect one state
to another or one state back to itself, and denote the specific changes in state. Each
state transition is unique, that is, given a certain set of circumstances (the overall
state of the system) a certain trigger even must result in exactly one new state.
3.4.5 Activity Diagram
Similar to a state diagrams, activity diagrams provide a way of understanding a
system based on the processes that occur within it. While a state diagram's main
Fig. 3.14
State icon (Harel
1987)
name
actions
Fig. 3.15 History icon
(Harel 1987)
H
Fig. 3.16
Nesting (Harel
superstate
1987)
state 1
state 1
state 1
