1. State Diagram – Advanced Concepts

2. Communications between objects
Objects communicate by sending messages to each other.
Messages are realized by events and transitions in state diagram.
The object that sends a message is said to generate an event.
Modeled by the action associated with the transition
The object that receives the message is said to realize / accept that event.

3. Communication between three state machines
GUI object
Open /
generateAccountNumber(act) ^
Account.open();
Database.openAccount(act)
Some State
Some other
State
Account object
open
Initial
Database object
openAccount (act) /
addAccount(act)
Some State
Communication between three state machines

4. Expanded syntax for transition
A transition is specified using the following syntax in order to show the communication between the objects
event-name (parameters) [guard] /
action-sequence ^ send-clause
where ‘send-clause’ is specified as
object.event-name (parameters); …

5. Messages shown in state diagrams
Remote Control On
Off On
Off
On()
Play
Stop
Off()
Play()
Stop()
CD Player On
Play
On & Play
Off
On & Stop
Off
Stop
Off

6. Simple and composite states
A state is composite, in contrast to a simple state, if it has a decomposition
UML Manual version 1.5
A composite state includes nested substates
A diagram for a composite state has two or more sub-diagrams connected by simple and/or concurrent transitions
The entry point of a substate is connected to the initial state of the substate
The exit point of a substate is connected to all final states of the substate

7. Composite state with or-substates
Running
Forward
Backward
The states of a running car

8. Or-substates Also called orthogonal states in UML 2.0
The composite state has two or more mutually exclusive substates
When the object is in the composite state, only one of the substates is active
In the previous diagram, the running car will be in ‘forward’ state or in ‘backward’ state at any time but not in both
Each substate can be explained by a separate state diagram

9. Composite state with and-substates
Running
Forward
Backward
Low Speed
High Speed
The states of a running car

10. And-substates Also called non-orthogonal states in UML 2.0
The composite state has two or more concurrent substates
When the object is in the composite state, every one of the concurrent substates is active
In the previous diagram, the running car will be in one of the four states: ‘forward & low speed’, ‘forward & high speed’, backward & low speed’ and ‘backward & high speed’
Each substate can be explained by a separate state diagram

11. Or-substates – Another Example
Eject
No CD loaded
Power ON [no CD]
Eject [CD in]
Power OFF
Power ON [CD in]
CD loaded

12. Expanded state diagram
No CD Loaded
Eject
CD drawer closed
CD drawer open
Power OFF
Power ON [no CD]
Eject [no CD]
Eject
Eject [CD in]
CD loaded
Power ON [CD in]
CD playing
Pause
CD paused
Pause or Play
Power OFF
Stop
Stop
CD stopped
Play

13. And-substates – another example
Student attending a course
Incomplete
Lab done
Lab done
Complete Lab 1
Complete Lab 2
passed
Project done
Complete Project
Complete Final exam
pass
fail
failed

14. Observation
If there is a transition from any one of the substates that lead to a state outside the composite state, then all the other concurrent substates terminate prematurely
The transition “fail” in the third substate illustrates this situation

15. State diagrams and specialization
Inheritance mechanism allows to redefine only behaviors of a superclass and not the structure of the superclass
The structure of a subclass must be the same or a superset of the structure of the superclass
Every state of a superclass object is also a valid state of the subclass object
The state diagram of a superclass can be inherited into the state diagram of a subclass

16. Composite State - Exercise
Draw a composite state diagram indicating the states of two phones when both of them are in use.
Hint: First identify the various values for the status of a single phone