1. CS251 – Software Engineering Lectures 11 State Diagrams
Read Reading 8
Chapter 8 (only 8.2) from OO SE 2/e,
Slides by: Timothy Lethbridge

2. Chapter 5: Modelling with classes
Last Lecture
Where are we now ?
why Modeling software ?
Sequence diagram ?
Chapter 5: Modelling with classes
© Lethbridge/Laganière 2012

3. Chapter 5: Modelling with classes
Outline
State diagrams
Modelling states and transitions
Modelling activities and actions
Examples
Chapter 5: Modelling with classes
© Lethbridge/Laganière 2012

4. Chapter 8: Modelling Interactions and Behaviour
8.2 State Diagrams
A state diagram describes the behavior of a system, some part of a system, or an individual object.
At any given point in time, the system or object is in a certain state.
Being in a state means that it is will behave in a specific way in response to any events that occur.
Some events will cause the system to change state.
In the new state, the system will behave in a different way to events.
A state diagram is a directed graph where the nodes are states and the arcs are transitions.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

5. State diagrams – an example
tic-tac-toe game
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

6. State diagrams – an example
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

7. Chapter 8: Modelling Interactions and Behaviour
States
At any given point in time, the system is in one state.
A state is represented by a set of values for the attributes of the given object.
It will remain in this state until an event occurs that causes it to change state.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

8. Chapter 8: Modelling Interactions and Behaviour
States
A state is represented by a rounded rectangle containing the name of the state.
Special states:
A black circle represents the start state
A circle with a ring around it represents an end state
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

9. Chapter 8: Modelling Interactions and Behaviour
State Diagram
States
Transitions
Events
Activities
Actions
Initial state
event
transition
state
off hook
Idle
Active
on hook
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

10. Chapter 8: Modelling Interactions and Behaviour
Transitions
A transition represents a change of state in response to an event.
The label on each transition is the event that causes the change of state.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

11. Example dial tone dialling idle digit (n) on-hook off-hook on-hook
State
Event
Transition
digit (n)
digit (n)
dial tone
dialling
on-hook
off-hook
on-hook
idle

12. State diagrams – an example with conditional transitions
action
condition

13. State diagrams – an example with conditional transitions
Add these info to the last state diagram (a) The course section can be canceled when in any state, except after it has been taught. (b) A student can drop out at any time, except after the course section has been taught.

14. Activities in state diagrams
An activity is something that takes place while the system is in a state.
It takes a period of time.
The system may take a transition out of the state in response to completion of the activity,
Some other outgoing transition may result in:
The interruption of the activity, and
An early exit from the state.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

15. State diagram – an example with activity
Audio Playing
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

16. Chapter 8: Modelling Interactions and Behaviour
Types of Events
External Event (also known as system event)
is caused by something outside the system boundary
e.g. when a cashier presses the “enter item” button on a POST, an external event has occurred.
Internal Event
is caused by something inside our system boundary.
In internal event arises when an operation is invoked via a message sent from another internal object.
Temporal Event
is caused by the occurrence of a specific date and time or passage of time.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

17. Actions in state diagrams
An action is something that takes place effectively instantaneously
When a particular transition is taken,
Upon entry into a particular state, or
Upon exit from a particular state
An action should consume no noticeable amount of time
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

18. State diagram – an example with actions
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

19. Nested substates and guard conditions
A state diagram can be nested inside a state.
The states of the inner diagram are called substates.
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

20. State diagram – an example with substates
Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

21. Chapter 8: Modelling Interactions and Behaviour
© Lethbridge/Laganière 2005

22. Example: Online Chess

24. ExampleOnline Chess

25. ESE — Modeling Behaviour
Example: Phone
ESE — Modeling Behaviour
© Oscar Nierstrasz

26. Chapter 5: Modelling with classes
Outline
State diagrams
Modelling states and transitions
Modelling activities and actions
Examples
Chapter 5: Modelling with classes
© Lethbridge/Laganière 2012

27. Chapter 5: Modelling with classes
Readings and Videos
Very Important
R8: Chapter 8 (Modeling interactions and behavior) of OOSE, 2nd ed by Timothy Lethbridge
Read section 8.2 from page 291 to page 301
Appendix A: Summary of UML Syntax – page 471 and 472
agram.htm
Chapter 5: Modelling with classes
© Lethbridge/Laganière 2012