State Diagrams

1
State Diagrams

• Pepper

2
Purpose

• Show behavior from the view of movement through
  different states.
• See how you can get to a certain state
• See how you can leave a certain state
• See all the actions that can be done while in a
  state

3
2 Lists State and Stimulus

• EX A course in a registration system
• State List Stimulus
  List

Stimulus Description
Create course Initializes the course
Register students Happens inside the open state.
Cancel the course Cancels an existing course but a record of the course existing remains. Tell students it cancels
Delete a course Delete a mistakenly created course
Fill a course Closes the course
Notify about cancelation Happens inside the canceled state
State Description
Initialized Exists, but no details set up
Open Ready for registration
Canceled
Closed
Deleted

4
Course State Diagram

• Credit to http//laser.inf.ethz.ch/2012/slides/
  Jacobson/UML20Past20Present20and20Future20Par
  t202.pdf

5
Words on the Line

• Trigger an action
• Guard (inside ) a condition
• Transitional behavior (after /) a message or
  variable setting

6
Summary

• Start with states
• List of state and stimulus helps you think of all
  different states
• Some actions may happen inside states and not be
  stimulus for movement
• Draw rounded boxes for states
• Look at each stimulus to see if it gets an arrow
  from that state.
• Not an activity diagram