Object-Oriented
Analysis and Design
Session 3b: Behavioral Modeling – State machine diagrams
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Outline
1.
2.
3.
4.
5.
6.
7.
8.
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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Introduction to State
Machine
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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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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.
ON
OFF
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What are Statecharts?
• Statecharts are visual formalism for
specifying behavior of complex systems.
• Developed by David Harel.
Employee
Working
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rest[break]
Resting
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State Machine (Automaton) Diagram
• Graphical rendering of automata behavior
on
Lamp On
on
off
off
Lamp Off
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Outputs and Actions
• As the automaton changes state it can
generate outputs:
on
Lamp On
print(”on”)
Lamp
On
on
on/print(”on”)
off
off
Lamp
Off
off
Mealy automaton
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on
Lamp
Off
off
Moore automaton
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Extended State Machines (1)
• Addition of variables (“extended state”)
on
ctr : Integer
Lamp On
on/ctr := ctr + 1
off
off
Lamp Off
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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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State Machine Diagrams
Syntax and Semantics
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State Machine Diagram
“top” state
Initial
pseudostate
State
top
Trigger
Ready
Transition
stop /ctr := 0
Final
state
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Done
Action
stop
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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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Initial and Final States
start
White’s
turn
Black wins
stalemate
white
moves
black
moves
Draw
stalemate
Black’s
turn
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checkmate
checkmate
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White wins
14
Activity and Action
• An activity:
–
–
–
–
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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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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Transitions
• A transition is enabled if the object is at a state
preceding the transition.
• An enabled transition is activated upon its trigger
activation.
E1
S1
E2
S2
S3
• An initial transition indicates that the default is
entering S2.
• A transition can connect the same state.
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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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Object Behavior and State Machines
• Direct mapping:
on
Initialize
Object
Lamp
On
Wait for
Event
Handle
Event
on/print(”on”)
off
Lamp
Off
Terminate
Object
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off
stop
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State Entry and Exit Actions
LampOn
entry/lamp.on();
e2
exit/lamp.off();
e1
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Order of Actions: Simple Case
• Entry actions are performed after (entering) transition actions.
• Exit actions are performed before (exiting) transition actions.
LampOn
entry/lamp.on();
off/printf(“to off”);
entry/lamp.off();
exit/printf(“exiting”);
exit/printf(“exiting”);
Resulting action sequence:
printf(“exiting”);
printf(“to off”);
lamp.off();
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LampOff
off/printf(“needless”);
printf(“exiting”);
printf(“needless”);
lamp.off();
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Internal Transitions
• Self-transitions that bypass entry and exit.
Internal
transition
actions
triggered by
an “off” event
LampOff
entry/lamp.off();
exit/printf(“exiting”);
off/null;
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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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Guards
• Conditional execution of transitions
– side-effect free
bid [value < 100] /reject
bid [value >= 200] /sell
Selling
Happy
bid [(value >= 100) & (value < 200)] /sell
Unhappy
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Guards and Events (1)
S1
S1
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E1
E1
S2
S2
Entered C
[C]
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S3
S3
25
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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Phone Line Example
on hook
on hook
Idle
off hook
on hook
Dial tone
do: sound dial tone
digit (n)
digit (n)
do: find connection
routed
do: play message
message done
Ringing
on hook / disconnect line
on hook
Recorded
message
Connecting
on hook
on hook
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valid number
busy
do: sound busy tone
Time out
invalid number
Dialing
Busy tone
time out
time out
called phone answers
/ connect line
Connected
called phone hangs up
/ disconnect line
Disconnected
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Static Conditional Branching
• Merely a graphical shortcut for convenient
rendering of decision trees.
Selling
Happy
bid
[value >= 200] /sell
[value < 100] /reject
[(value >= 100) & (value < 200)] /sell
Unhappy
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Dynamic Conditional Branching
• Choice pseudostate: guards are evaluated
only when the decision point is reached.
Selling
Happy
bid /gain := calculatePotentialGain(value)
[gain >= 200] /sell
[gain < 100] /reject
[(gain >= 100) & (gain < 200)] /sell
Dynamic
choicepoint
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Unhappy
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State Hierarchy
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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.
Indentation-status
The states in an
IndentationStatus statechart:
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On
Left
Right
Center
Justify
Off
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States Hierarchy (2)
States hierarchy is used for describing different
levels of abstraction.
High Level
Detailed Level
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States Hierarchy (3)
States hierarchy is used for clustering.
Un clustered
clustered
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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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States Hierarchy (5)
• Graduated attack on complexity
– states decomposed into state machines
LampOff
entry/lamp.off()
flash/
LampFlashing
FlashOn
entry/lamp.on()
off/
1sec/
on/
LampOn
1sec/
on/
on/
FlashOff
entry/lamp.off()
entry/lamp.on()
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States Hierarchy (6)
• Higher-level transitions
LampOff
entry/lamp.off()
flash/
Default transition to
the initial pseudostate
LampFlashing
FlashOn
entry/lamp.on()
off/
1sec/
1sec/
on/
LampOn
on/
FlashOff
entry/lamp.off()
entry/lamp.on()
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States Hierarchy (7)
• Triggered by a completion event
– generated automatically when an immediately
nested state machine terminates.
Committing
completion
transition (no trigger)
Phase1
CommitDone
Phase2
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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/
on/
off/
FlashOff
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States Hierarchy (9)
• Same approach as for the simple case
S1
exit/exS1
S2
entry/enS2
initS2
S11
exit/exS11
E/actE
S21
entry/enS21
Actions execution sequence:
exS11 exS1  actEenS2  initS2  enS21
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State History
Mechanism
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History Mechanism (1)
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History Mechanism (2)
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History Mechanism (3)
G
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History Mechanism (4)
• Return to a previously visited hierarchical state
– deep and shallow history options
Diagnosing
suspend/
resume/
H*
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Diagnostic1
Diagnostic2
Step11
Step21
Step12
Step22
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State Concurrency
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Orthogonality and Concurrency (1)
• Multiple simultaneous perspectives on the same
entity
age
employee
Child
Staff
Member
Adult
Manager
Retiree
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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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Orthogonality and Concurrency (3)
• Combine multiple simultaneous descriptions
age
employee
Child
Staff
Member
Adult
age
Retiree
Manager
Child
Adult
Retiree
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employee
Staff
Member
Manager
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Orthogonality and Concurrency (4)
A
D
B
a
d
g
b
G
m
g
B,G
a
a
g
m
F
d
B,F
a
C,E
Use of
Orthogonal Regions
a
(in G)
C
B,E
m
E
a
C,F
No Use of
Orthogonal Regions
b
C,G
d
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Orthogonality and Concurrency (5)
• All mutually orthogonal regions detect the same
events and respond to them “simultaneously”.
legalStatus
LawAbiding
robBank/
Outlaw
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financialStatus
Poor
robBank/
Rich
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Orthogonality and Concurrency (6)
• Typically through shared variables or
awareness of other regions’ state changes.
sane : Boolean
flying : Boolean
Catch22
sanityStatus
flightStatus
Crazy
Flying
entry/sane := false;
entry/flying := true;
(flying)/
request
Grounding/
(sane)/
(~sane)/
Sane
Grounded
entry/sane := true;
entry/flying := false;
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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
b/d
C
a/c
B
d/a
c/b
D
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Transition Forks and Joins
• For transitions into/out of orthogonal
regions:
age
Child
Staff
Member
Adult
Retiree
Manager
employee
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Reducing Multiple Transitions (1)
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Reducing Multiple Transitions (2)
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Concluding Example
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Mini Organ Example (1)
ON\OFF
a
Display
STYLE
SONG
b
c
1
2
3
4
5
6
7
8
9
Name
Mode
Number
START
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Mini Organ Example (2)
1. The button a is used for switch the organ on and off
2. 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.
3. 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).
4. 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).
5. 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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Mini Organ Example (3)
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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Mini Organ Example (4)
on
play
mode
song#
style#
display
a
disp-mode
disable
off
a
s or
songend
s
style
b [c2]
1
1
1[c1]
enable
Do: if song# in
k and style# in
m then play
song k in style
m
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style
c
b
1[c2]
song
j
name
song
number
w
i
x [c4]
j[c1]
c [c1]
k
y [c3]
i[c2]
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State Machine and UML
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Dishwasher – Class Diagram
Dishwasher
cycles : int
rinseTime : int
washTime : int
dryTime : int
Tank
1
itsTank
evTankDrain()
evTankFill()
Dishwasher()
setup()
evStart()
evOpen()
evClose()
evQuick()
evNormal()
evIntensive()
evService()
Jet
1
itsJet
evJetOff()
evJetSpray()
evJetPulse()
itsHeater 1
Heater
evHeaterOff()
evHeaterOn()
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Dishwasher – State Machine Diagram
AcmeHeater
Dishwasher
AcmeJet
off
evHeaterOn
evHeaterOff
idle
on
evJetSpray
AcmeTank
evTankFill
evJetOff
running
tm(4000)/
itsDishwasher->GEN(evFull);
filling
spraying
empty>
tm(4000)/
itsDishwasher->GEN(evEmpty);
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evJetPulse
pulsing
full>
draining
evTankDrain
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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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