UML Statechart Diagrams

Statechart Diagrams

✱A Statechart Diagrams illustrates a state machine, highlighting the flow of control from one state to another state.

Contents

➤Simple states and composite states

➤Transitions, including events and actions

Uses

To model reactive objects

Common Modeling Techniques

Modeling Reactive Objects To model a reactive object:

A class, a use case or the system as a whole can be modeled as a state machine
Select the initial and final states for the object
Indicate the pre and the post conditions of the initial and the final states that define what the modeled component (class, use case, etc.) should do
Establish the stable states of the object by considering the conditions in which the object may be present for some significant amount of time
Starting with the high level states of the object, identify their substates
Decide on the significant partial ordering of stable states over the lifetime of the object
Decide on the events that trigger the transitions from one state to another state
Model these events as triggers to different transitions that shift from one legal ordering of states to another
Add actions to these transitions/states. Find out ways to simplify the machine by the use of branches, joins, forks, history states, and substates
Make sure that all the states are reachable with some sequence of events and their corresponding transitions
Verify that no state is a dead end from which no sequence of events will transition the object out of that state
Trace through the state machine, either manually or by using the tools so as to check it against important sequences of events and their responses
The image shows the statechart diagram for determining a simple context-free language message : '<' string '>' string ';'
The first string indicates a tag; the second string represents the body of the message

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