1. Object-Oriented Analysis and Design
Session 3b: Behavioral Modeling – State machine diagrams
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2. Outline Introduction to State Machine.……………..……... 3
State Machine Diagrams Syntax and Semantics….11
State Hierarchy………………………………...….31
State History Mechanism ………………...……....41
State Concurrency ……………………….……….46
Concluding Example ……………………………..57
State Machine Diagrams and UML ……..……….62
Summary ……………………………………...….65
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3. Introduction to State Machine
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4. Characterization of reactive systems
Continuous interaction with the environment
inputs and outputs are asynchronous in time.
Respond to interrupts.
Stringent time requirements.
Multiple possible scenarios of operation, depending on the history of previous behavior.
Based on interacting processes that operate in parallel.
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5. Automata
A machine whose output behavior is not only a direct consequence of the current input, but also of some past history of its inputs.
Characterized by an internal state which represents this past experience.
OFF ON
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6. What are Statecharts?
Statecharts are visual formalism for specifying behavior of complex systems.
Developed by David Harel.
Employee
rest[break]
Working
Resting
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7. State Machine (Automaton) Diagram
Graphical rendering of automata behavior on
Lamp On
off on
off
Lamp Off
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8. Outputs and Actions
As the automaton changes state it can generate outputs: on
off
Lamp On
Lamp Off
on/print(”on”)
Mealy automaton on
off
Lamp On
print(”on”)
Lamp Off
Moore automaton
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9. Extended State Machines (1)
Addition of variables (“extended state”)
off on
Lamp On
Lamp Off
on/ctr := ctr + 1
ctr : Integer
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10. Extended State Machines (2)
An extended (Mealy) state machine is defined by:
a set of input signals (input alphabet)
a set of output signals (output alphabet)
a set of states
a set of transitions
triggering signal
action
a set of extended state variables
an initial state designation
a set of final states (if terminating automaton)
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11. State Machine Diagrams Syntax and Semantics
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12. State Machine Diagram Ready stop /ctr := 0 Done stop “top” state State
Initial
pseudostate
top
Trigger
Ready
Transition
stop
/ctr := 0
Done
Final
state
Action
stop
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13. Statechart Diagram Elements
States
Any component or object within the system can be at a specific state in a given time.
When holding the state, an object (or a component) can perform activities (which can be interrupted).
Transitions
Specification of rules for moving between states.
A transition may consist of a trigger, condition, and an action.
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14. Initial and Final States
start
White’s
turn
checkmate
Black wins
stalemate
black
moves
white
moves
Draw
stalemate
Black’s
turn
White wins
checkmate
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15. Activity and Action An activity: An action:
can be performed within a state.
can be continuous.
can be sequential.
takes time.
An action:
can be performed within a state or during a transition.
can not be interrupted.
is atomic.
can take time.
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16. Event-Driven Behavior
Event = a type of observable occurrence
interactions:
object operation invocation (call event).
asynchronous signal reception (signal event).
occurrence of time instants (time event)
interval expiry.
calendar/clock time.
change in value of some entity (change event).
Event Instance = an instance of an event (type)
occurs at a particular time instant and has no duration.
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17. Transitions
A transition is enabled if the object is at a state preceding the transition.
An enabled transition is activated upon its trigger activation.
An initial transition indicates that the default is entering S2.
A transition can connect the same state. S3 S1 S2 E1 E2
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18. Object Behavior - General Model
Simple server model:
Initialize Object
Handling depends on
specific request type
Wait for Request
void:offHook (); {busy = true; obj.reqDialtone(); … };
Handle Request
Terminate Object
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19. Object Behavior and State Machines
Direct mapping: on
off
Lamp On
Lamp Off
on/print(”on”)
stop
Handle Event
Initialize Object
Terminate Object
Wait for Event
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20. State Entry and Exit Actions
LampOn e2
entry/lamp.on();
exit/lamp.off(); e1
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21. Order of Actions: Simple Case
Entry actions are performed after (entering) transition actions.
Exit actions are performed before (exiting) transition actions.
off/printf(“to off”);
LampOff
entry/lamp.off();
exit/printf(“exiting”);
LampOn
entry/lamp.on();
off/printf(“needless”);
Resulting action sequence:
printf(“exiting”);
printf(“to off”);
lamp.off();
printf(“exiting”);
printf(“needless”);
lamp.off();
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22. exit/printf(“exiting”);
Internal Transitions
Self-transitions that bypass entry and exit. actions
Internal transition
triggered by
an “off” event
LampOff
entry/lamp.off();
exit/printf(“exiting”);
off/null;
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23. State (“Do”) Activities
Forks a concurrent thread that executes until:
the action completes or
the state is exited.
“do” activity
Error
entry/printf(“error!”)
do/while (true) alarm.ring();
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24. Guards Conditional execution of transitions side-effect free Selling
bid [value < 100] /reject
Selling
Happy
bid [value >= 200] /sell
Unhappy
bid [(value >= 100) & (value < 200)] /sell
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25. Guards and Events (1) S1 S2 E1 S3 Entered C S1 S2 E1 S3 [C]
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26. Guards and Events (2) Special operators in(a) – means in state a.
en(b) – means the occurrence of entering state b.
ex(c) – means the occurrence of exiting state c.
tm(min) – means trigger if min time units have passed.
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27. on hook / disconnect line
Phone Line Example
Idle
Dialing
off hook
digit (n)
valid number
Ringing
routed
Connected
called phone answers
/ connect line
Disconnected
called phone hangs up
/ disconnect line
Time out
time out
invalid number
on hook
busy
message done
Dial tone
do: sound dial tone
Connecting
do: find connection
Recorded
message
do: play message
Busy tone
do: sound busy tone
on hook / disconnect line
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28. Static Conditional Branching
Merely a graphical shortcut for convenient rendering of decision trees.
Selling
Unhappy
Happy
bid
[value >= 200] /sell
[value < 100] /reject
[(value >= 100) & (value < 200)] /sell
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29. Dynamic Conditional Branching
Choice pseudostate: guards are evaluated only when the decision point is reached.
Selling
Unhappy
Happy
bid /gain := calculatePotentialGain(value)
[gain >= 200] /sell
[gain < 100] /reject
[(gain >= 100) & (gain < 200)] /sell
Dynamic
choicepoint
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30. State Hierarchy
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31. States Hierarchy (1)
Intended to cluster together alternative states of a single aspect / object.
Results: OR states. An OR state is a super-state of its sub-states.
A state that has no sub-states is a basic state.
The states in an IndentationStatus statechart:
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32. States Hierarchy (2)
States hierarchy is used for describing different levels of abstraction.
High Level
Detailed Level
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33. States Hierarchy (3) States hierarchy is used for clustering.
Un clustered
clustered
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34. States Hierarchy (4) Initial States– one per state.
To be in a state is to be in ONE of its sub states.
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35. States Hierarchy (5) Graduated attack on complexity
states decomposed into state machines
off/
LampOff
entry/lamp.off()
LampOn
entry/lamp.on()
on/
LampFlashing
flash/
1sec/
FlashOff
entry/lamp.off()
FlashOn
entry/lamp.on()
on/
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36. the initial pseudostate
States Hierarchy (6)
Default transition to
the initial pseudostate
Higher-level transitions
off/
LampOff
entry/lamp.off()
LampOn
entry/lamp.on()
on/
LampFlashing
flash/
1sec/
FlashOff
entry/lamp.off()
FlashOn
entry/lamp.on()
on/
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37. transition (no trigger)
States Hierarchy (7)
Triggered by a completion event
generated automatically when an immediately nested state machine terminates.
completion
transition (no trigger)
Committing
Phase1
Phase2
CommitDone
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38. States Hierarchy (8)
Two or more transitions may have the same triggered event
inner transition takes precedence.
if no transition is triggered, event is discarded.
LampFlashing
FlashOn
on/
off/
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FlashOff

39. Actions execution sequence:
States Hierarchy (9)
Same approach as for the simple case S1
exit/exS1 S2
entry/enS2
initS2
E/actE
S11
exit/exS11
S21
entry/enS21
Actions execution sequence:
exS11 exS1  actEenS2  initS2  enS21
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40. State History Mechanism
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41. History Mechanism (1)
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42. History Mechanism (2)
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43. History Mechanism (3) G
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44. History Mechanism (4)
Return to a previously visited hierarchical state
deep and shallow history options
Diagnosing
suspend/
Diagnostic1
Diagnostic2
Step11
Step12
Step21
Step22
resume/ H*
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45. State Concurrency
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46. Orthogonality and Concurrency (1)
Multiple simultaneous perspectives on the same entity
Child
Adult
Retiree
age
Staff
Member
Manager
employee
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47. Orthogonality and Concurrency (2)
Describe independent components of a behavior.
Behavior of parts of an aggregate object.
Enforce synchronization of concurrent activities.
Concurrency is an AND-decomposition of a state.
To be in a state S is to be in ALL of its components. S is an AND state.
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48. Orthogonality and Concurrency (3)
Combine multiple simultaneous descriptions
Child
Adult
Retiree
age
Staff
Member
Manager
employee
Staff
Member
Manager
employee
Child
Adult
Retiree
age
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49. Orthogonality and Concurrency (4)B C E G F A D a b g d m
(in G)
Use of
Orthogonal Regions
C,F
C,E
C,G
B,G
B,E
B,F a b g d m
No Use of
Orthogonal Regions

50. Orthogonality and Concurrency (5)
All mutually orthogonal regions detect the same events and respond to them “simultaneously”.
Outlaw
LawAbiding
Poor
Rich
financialStatus
legalStatus
robBank/
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51. Orthogonality and Concurrency (6)
Typically through shared variables or awareness of other regions’ state changes.
sane : Boolean
flying : Boolean
Catch22
sanityStatus
flightStatus
(flying)/
Crazy
entry/sane := false;
Sane
entry/sane := true;
request
Grounding/
Flying
entry/flying := true;
Grounded
entry/flying := false;
(sane)/
(~sane)/
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52. Transition Sequence A transition might be a trigger
An event can trigger additional transitions
Several transition can be triggered within a single step
Solution
The number of triggered transition should be limited A C
b/d
a/c
d/a
c/b B D

53. Transition Forks and Joins
For transitions into/out of orthogonal regions:
Staff
Member
employee
Child
Adult
Retiree
age
Manager
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54. Reducing Multiple Transitions (1)
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55. Reducing Multiple Transitions (2)
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56. Concluding Example
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57. Mini Organ Example (1)
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58. Mini Organ Example (2)
The button a is used for switch the organ on and off
The organ enables a song selection and its style. When the organ is turned on the display shows the mode: STYLE or SONG and its number. The default is song #1/sytle #1 and the mode is STYLE.
To select a style one need to press the b button and the required style number (1-9). Each style has a function that return its name – StyleName(x).
To select a song one need to press the c button and the required song number(1-9). Each song has a function that return its name – SongName(x).
Pressing the start button plays the current song following the current style. Another press stop the music. It is possible to change the song or style during music playing.
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59. Mini Organ Example (3) a - pressing the a button
Events
a - pressing the a button
b - pressing the b button
c - pressing the c button
s - pressing the START button
i - pressing the a digit button (2-9)
1 - pressing the 1 button
songend – end of song playing
Variables
i,j – can get values between 2-9
k,m – can get values between 1-9
w – can get a song or style name
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60. Mini Organ Example (4) c b x y
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61. State Machine and UML
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62. Dishwasher – Class Diagram
Tank
evTankDrain()
evTankFill()
Dishwasher
cycles : int
rinseTime : int
washTime : int
dryTime : int
Dishwasher()
setup()
evStart()
evOpen()
evClose()
evQuick()
evNormal()
evIntensive()
evService()
Jet
evJetOff()
evJetSpray()
evJetPulse()
Heater
evHeaterOff()
evHeaterOn()
itsTank 1
itsJet
itsHeater
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63. Dishwasher – State Machine Diagram
AcmeHeater
AcmeJet
off on
evHeaterOn
evHeaterOff
running
pulsing
spraying
idle
evJetPulse
evJetOff
evJetSpray
Dishwasher
AcmeTank
draining
filling
full>
empty>
tm(4000)/
itsDishwasher->GEN(evFull);
evTankFill
itsDishwasher->GEN(evEmpty);
evTankDrain
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64. Summary UML uses a variant of Harel’s statecharts
adjusted to software modeling needs
Used to model event-driven (reactive) behavior
well-suited to the server model inherent in the object paradigm
Includes a number of sophisticated features that realize common state-machine usage patterns:
entry/exit actions
state activities
dynamic and static conditional branching
Also, provides hierarchical modeling for dealing with very complex systems
hierarchical states
hierarchical transitions
orthogonality
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