Event Driven Modeling

The event driven modeling is a programming technique in which system response to external and internal events such as user actions, mouse clicks, key pressing, message from other threads on the based of an events the flow of the program is determined.  The event driven modeling technique is based on the thinks that the system has a finite state and event is a reason of moving from one state to another state. The graphical user interfaces and other applications (e.g. java script, web application) use event driven programming techniques to performing certain type of action in response to a user action.

 UML support event driven modeling using state diagram which is based on statecharts (Harel, 1987, 1988).  State diagram is a diagram that is used to describe the behavior of the system and state diagrams are used to give an abstraction view of the behavior of the system. State diagram consist of a finite number of state (represents objects of a class) and transition from one state to another is caused by an event. State diagram do not show the flow of data within the system.

 An example of simple microwave oven to illustrate an event driven modeling. Actually real microwave ovens are more complex then this system but this simple system is easier to understand.

                           State diagram of a microwave oven

In UML rounded rectangle represent state of a system. They include a description of the action that is taken following “do”. The labeled arrows represent the stimuli that caused the transition from one state to another. Filled circle represent a start and end states of the system.

State and stimuli for the microwave oven

State                                   Description

Waiting                       The oven is waiting for input. The display show current time.

Half power                  The oven power is set to 300 watts.

Full power                   The oven power is set to 600 watts.

Set time                      The cooking time is set to the user input time. The display show

                                   the cooking time selected and is updated as the time is set.

Enabled                     Oven operation is enabled. Interior oven light is off. Display shows     

                                    ‘Ready’

Disabled                     Oven operation is disabled for safety. Interior light is on.

                                    Display shows ‘not ready’.

Operation                   Oven in operation, Interior light is on. Display shows the timer

                                    countdown.  On completion of cooking the buzzer is sounded for

                                     5 sec. oven light is on. Display shows ‘cooking complete’ when

                                      buzzer is sounding.

Stimuli                               Description

Half power                         the user has pressed the half power.

Full power                         the user has pressed the full power.

Timer                                the user has pressed one of the timer button.

Number                            the user has pressed the numeric key.

Door open                        the oven door switch is not closed.

Door closed                      the oven door switch is closed.

Start                                 the user has pressed the start button.

Cancel                             the user has pressed the cancel.