1. Chapter 5 state Modeling

2. 5. State Modeling
State Model consists of multiple state diagrams – one for each class with important temporal behavior
State diagrams relate events and states
Events
States
Transitions and Conditions
State Diagram
State Diagram Behavior

3. 5.1 events An occurrence at a point in time
Happens instantaneously with regard to the time scale of an application
Two events that are causally unrelated are said to be concurrent – no effect on each other
Events include error conditions & normal occurrences
Examples : Transaction Aborted ; Time Out
Three Kinds of Events
Signal Event
Change Event
Time Event

4. 5.1 Three Kinds of events 5.1.1 Signal Event
Signal : An explicit message - one way transmission of info from one object to another
Example Traffic Light
Signal event : It’s an occurrence in time
UML Notation of Signal in a class
Keyword “Signal” in guilemets << >>
5.1.2 Change Event
A event that is caused by the satisfaction of a boolean expression
UML Notation
Keyword “when” followed by paranthesized boolean expression
When (battery power < lowerlimit)
5.1.3 Time Event
An event that is caused by the occurrence of an absolute time or the elapse of a time interval
Keyword “when” - in parathesis expression involving time
Eg: when (date = September )
Keyword “after” - in paranthesis expression that evaluates to a time duration
Eg: after (10 seconds)

5. 5.2 States An abstraction of the values & links of an object
Often a verb with a suffix of “ing”
Phone states - Waiting; Dialing
UML Notation
A rounded box containing a optional state name
Convention: State name in bold, center & near the top of the box with Capitalize
Various Characterization of States - Refer Book

6. 5.3 Transitions & Guard conditions
Transition: Instantaneous change from one state to another
Guard Conditions(GC): Boolean expression that must be true in order for a transition to occur
UML Notation:
Transition: A line from the origin state to the target state. An arrow head points to the target.
Guard Condition: Optionally listed in square brackets
A GC triggers only once is different from Change Event which needs to be satisfies all time.

7. 5.4 state diagram
A graph whose nodes are states & whose arcs are transition between states
State names must be unique within the scope of a state diagram
UML Notation
A state diagram is a rectangle with its name in a small pentagonal tag in the upper left corner
5.4.1 Sample State Diagram
5.4.2 One shot State Diagram
Represents Object with finite lives and have initial & final states

8. 5.5 StATE DIAGRAM BEHAVIOR 5.5.1 Activity Effects
Activity: Actual behavior that can be worked by any number of effect
Effect: A reference to a behavior that is executed in response to an event
An activity may be performed upon a transition or event within a state
UML Notation
“/” & the name of the activity following the event that causes it
“do” keyword for ongoing activity

9. 5.5.2 do activities
A do activity is an activity that continues for an extended time
A do activity can only occur within a state & cannot be attached to a transition

10. 5.5.3 Entry & exit activities
Activities can be bound to entry or to exit from a state or on transition
If a state has multiple activities they are performed in order
Activities on incoming transition
Entry activities
Do activities
Exit activities
Activities on the outgoing transition
Any event can occur within a state & cause an activity to be performed
Self transition: Causes entry & exit activities to be executed

11. 5.5.4 Completion transition
An arrow without an event name indicates an automatic transition that fires when the activity associated with the source state is completed
Such unlabelled transition are called completion transition as they are triggered by completion of activity in the source state

12. 5.5.5 Sending signals
From one object if a signal is sent to another object
If an object can receive signals from more than one object the order in which concurrent signals are received may affect the final state. This is called race condition