Dynamic Modeling

Grady Booch, James Rumbaugh, and Ivar Jacobson, The Unified Modeling Language User Guide, 2nd edition, Addison Wesley, 2005.

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Outline

• Dynamic models• State machine diagrams (a.k.a. statechart)

– Modeling object or system states

• Interaction diagrams– Sequence diagrams (a.k.a. message sequence)

• The time order of interactions between objects

– Communication diagrams (a.k.a. collaboration)• Messages passed between objects

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Dynamic Models

• Used to model control aspects (e.g., when)• Several different models possible, e.g.,

– Focusing on state changes– Focusing on interactions

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Dynamic Models

• Used to model control aspects (e.g., when)• Several different models possible, e.g.,

– Focusing on state changes• Used to show software control• Sequence of operations and events• Transitions between states• UML state machine diagrams

– Focusing on interactions

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Dynamic Models

• Used to model control aspects (e.g., when)• Several different models possible, e.g.,

– Focusing on state changes– Focusing on interactions

• Used to show dynamic relationships between objects • Messages, interfaces, and timings• UML interaction diagrams

– Sequence diagrams, focusing on ordered interactions

– Communication diagrams, focusing on interaction links

– Timing diagrams, focusing on interaction timings

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Outline

Dynamic models• State machine diagrams• Interaction diagrams

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Modeling State Changes

• Modeling object/system states– UML state machine diagram– Depicts the flow of control using states and

transitions by describing• How an object or system changes over time• Event (e.g., operation calls) it may respond to• How it respond to them

– Generalization of finite state machines

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Modeling Object States

• Network of states and transitions• One diagram for each object with important

dynamic behavior• Independent timing of state machines for

different objects (asynchronous)

On Off

switch pushed

switch pushed

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Elements of State Machine Diagrams

Idle

Initial State

Running

Final State

State

Transition

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Initial and Final States

White’s turn

Black’s turn

blackmoved

whitemoved

start

Blackwin

Draw

Whitewin

checkmate

checkmate

stalemate

stalemate

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States

• Some phase during the lifetime of an object that is significant of its behavior (e.g., observable or different behavior)

• Condition or situation in the life of a system (or object) during which it:– Satisfies some condition (i.e., state invariant),

– Performs some activity, or

– Waits for some events.• Set of values of properties that affect the behavior of the system

(or object).– Determines response to an event

– Thus, different states may produce different responses to the same event

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States (Cont.)

• All objects have states.• A state is an abstraction of the values

maintained by the object that determine behavior.

• Examples:– The invoice is paid.– The car is parked.– The engine is running.– Kate is working.– Jim is playing.

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State Corresponds to Interval of Time between Events

• Events: points in time• State: interval of time; may correspond

to a continuous activity– E.g., waiting, ringing, and flying

• State may be associated with value of object satisfying some condition.– E.g., automobile transmission is in reverse.– E.g., balance of account is negative

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Identifying States

• Ignore attributes that don't affect behavior

• Combine set of attributes that form a parameter of the control– E.g., the control is not changed by

changing the digits in the phone call.

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Specifying States• Name (optional)• Internal activities (optional)

– Actions and activities performed while in the state– Predefined: entry, exit, do

• Internal transitions (optional)– Reaction within a state but without changing state

Brewing

do / brew coffee

pot removed/ suspendpot replaced/ resume

Name

Internal activities

Internal transitions

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Internal Activities and Transitions

• Actions and activities performed while in the state– Action: atomic– Activity: more complex behavior

• Action/activity label, specifying triggering conditions– Entry: performed on entry to state– Exit: performed on exit from state– Do: performed while in the state

• Internal transitions– Reactions to events that doesn’t

cause state changes (see transitions)

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Attacking

entry/unsheathe sworddo/chargeexit/sheathe sword

enemy swings[distance<3 ft]/dodge

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Example

Starting

entry / start dial toneexit / end dial tone

Dialing

entry / number.append(n)

dialed (n)

dialed (n)

[number.isValid()]

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Events

• Something that happens at a point in time– No duration: instantaneous– At least we think of it this way when we model

(abstraction)

• Stimulus from one object to another• May result in a change of state• May result in event being sent to another

object

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Two Events:

• May be unrelated (concurrent)– E.g., flight 123 departs El Paso and flight

555 departs Las Vegas.

• May depend on each other (sequential)– E.g., flight 123 departs El Paso and flight

123 arrives Las Vegas.

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Transitions

• Relationship between two states indicating that a system (or object) in the first state will:– Perform certain actions and– Enter the second state when specified event

occurs and specified condition is satisfied.• Consists of:

– Source and target states– Optional event trigger, guard condition, and action

Sourcetrigger [guard] / action

Target

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Transitions (Cont.)

• Source state– State affected by transition

• Event trigger– Triggering the transition

• Guard condition– Boolean evaluated after the

event trigger. Transition only occurs if guard is true

• Action– Atomic operation that occurs as

the transition occurs• Target state

– State active after transition

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Source

trigger [guard] / action

Target

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Example

keyPressed(key) [key == ENTER_KEY] / str := inputBuffer

Note that every transition should be labeled.

Sourcetrigger [guard] / action

Target

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Transitions (Cont.)

• Lead from one state to another• Instantaneous• Several types of events:

– A condition becomes true.– An explicit signal is received from an object.– An operation is called by an object.– A designated period of time passes.

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Phone Example

digit dialed (n)[incomplete]

Dialing Connecting

busy

connected

digit dialed (n)[valid] / connectdigit dialed (n)

[invalid]

Invalid

Ringing

Busy

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Protocol vs. Behavior Machines

• Protocol state machine– Specifies the intended pattern of calls on an object by specifying

• which operations of the object can be called in which state

• and under which condition, thus specifying the allowed call sequences on the object's operations.

– Describes an object's life cycle.

– Post-conditions are used instead of actions

• Behavior state machine– Expresses the behavior of part of a system, e.g., to define object

and operation behavior

– Actions are used instead of post-conditions

– States can have actions (entry, exit, do)

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Protocol State Machine

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Not Overdrawn[balance >= 0]

Overdrawn[balance < 0]

credit(x)

debit(x)[balance - x >= 0]

credit(x)[balance + x >= 0]

credit(x)[balance + x >= 0]

debit(x)[balance - x < 0]

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Protocol State Machine

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Not Overdrawn[balance >= 0]

Overdrawn[balance < 0]

credit(x)

debit(x)[balance - x >= 0]

credit(x)[balance + x >= 0]

credit(x)[balance + x >= 0]

debit(x)[balance - x < 0]

Account

-balance: Integer

+ balance(): Integer+ credit(x:Integer): void+ debit(x:Integer): void

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In Class: Digital Watch

• (Pairs) Draw a state machine diagram

The watch has a single mode button and a single advance button. Pressing the mode button once and then pressing the advance button increments the hours by 1. Each press of the advance button increments the hour. Pressing the mode button the second time allows advancing the minutes by one. Pressing the mode button a third time displays the current time. While displaying the current time, the advance button is ignored. Pressing the mode button allows the user to set the hour again.

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In Class: Toy Train (Pairs) Draw a state machine diagram

Initially, headlight is off, and train is not moving. If power on, headlight shines, and train moves forward. If power off, headlight goes out, but train still moves forward. If power on, headlight comes on, and train does not move. If power off, headlight goes off, and train stays stopped. If power on, headlight comes on, and train moves backward. If power off, headlight goes off, but train still moves backward. If power on, headlight comes on, and train doesn’t move. If power off, headlight off, and train remains stopped. Repeats from step 2 above.

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Structuring State Machine Diagrams

anomalyNormal Recovery

Identification

PressureRecovery

TemperatureRecovery

recovery success

recovery success

recovery success

temperatureproblem

pressureproblem

recovery failure

recoveryfailure

recoveryfailure

Can this diagram be presented better?

Unstructured!

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Better Presented:

anomaly

Normal RecoveryIdentification

PressureRecovery

TemperatureRecovery

recoverysuccess temperature

problempressureproblem

Recovery

recoveryfailure

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Composite States (Cont.)

• States containing one or more state diagrams• Used to simplify diagrams• Inside, looks like state machine diagrams• May have composite transitions• May have transitions from substates• May have "history states" (H symbol)

denoting the most recently occupied state• Sequential (OR) and parallel (AND) states

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Composite States and Transitions

Idle

Maintenance

Printing

Selecting Processing

Validating

Transition from substate

Transition to/from composite state

Active

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H

Transition to history state

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Example of Composite State

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Including Composite States

Starting

entry / start dial toneexit / end dial tone

Partial Dialing

entry / number.append(n)

dialed(n)

dialedn)

[number.isValid()]

Dialing

Dialing Number

Include / Dialing

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Sequential (OR) and Parallel (AND) States

• States can be divided into concurrent parts, called “regions”.

• OR state: composite state with single region• AND state: composite state with multiple

regions– System is in all regions of the state, i.e., executes

concurrently.

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Example of AND State

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Synchronization

• Concurrency (split of control)

• Synchronization

substate1 substate2

Superstate

substate3 substate4

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Example

Idle

Command

Testing

Waiting

Diagnose

Join

ForkComposite state

Maintaining

Testing

Commanding

Concurrent regions

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Another Example

HW1 HW2

Incomplete

Project

Midterm Final

Passed

Failedfail

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Example of Synchronization

Remote Control

Off OnOn

Off

Play

Stop

On/Stop On/PlayOff

On

Off

Off/Stop

Play

Stop

MP3 Player

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In Class: Avoiding Combinatorial Explosion of States

(Pairs) A car can be in the state of moving or stop. It can also be clean or dirty. Model the states of a car:• without using parallel states• using parallel states

What will happen if we add a third property (say, Red vs. Blue) and a fourth property (say, Enclosed vs. Convertible)?

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In Class: Toy Train (Pairs) Draw a state machine diagram

Initially, headlight is off, and train is not moving. If power on, headlight shines, and train moves forward. If power off, headlight goes out, but train still moves forward. If power on, headlight comes on, and train does not move. If power off, headlight goes off, and train stays stopped. If power on, headlight comes on, and train moves backward. If power off, headlight goes off, but train still moves backward. If power on, headlight comes on, and train doesn’t move. If power off, headlight off, and train remains stopped. Repeats from step 2 above.

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In Class: Office Phone

• (Pairs) Draw a state machine diagram describing the operation of an office phone.

Assume that the phone has keys for the digits 0-9, #, and *. It can detect when the receiver is on-hook or off-hook. The phone is idle when the receiver is on-hook. Model phone calls.– making calls (e.g., dialing, connecting,

talking), – receiving calls (e.g., ringing, talking)

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Outline

Dynamic modelsState machine diagrams• Interaction diagrams

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Modeling Interactions

• Focus on communications among elements– Ordering of interactions– Messages and interfaces– Communication links– Timings of messages (between when

message sent and received)

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UML Interaction Diagrams

• Whole class of diagrams including– Sequence Diagrams

• The time order of interactions between objects

– Communication Diagrams• Messages passed between objects

– Interaction Overview Diagram• Overview diagram that hides much of the detail

– Timing Diagram • Interactions with precise time axis (for real-time or time-

sensitive systems)

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Sequence Diagrams

• Depicts object interaction by highlighting the time ordering of method invocations

• Describes a sequence of method calls among objects

• (This is the only interaction diagram we’ll look at.)

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Example

: Customer : Order : Payment : Product : Supplier

place an order

process

validate

deliver

if ( payment ok )

back order

if ( not in stock )

get address

mail to address

message

lifetimecontrol

object

sdPlaceOrder

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Example (Cont.)

: Customer : Order : Payment : Product : Supplier

place an order

process

validate

deliver

if ( payment ok )

back order

if ( not in stock )

get address

mail to address

Sequence of message sending

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Different Types of Messages

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o: Class

Synchronous message

Asynchronous message

Return message

Creation message

Destruction message

<<create>>

<<destroy>>

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Return MessagessdPlaceOrder

:CustomerWIndow :Customer

ChangeUpdate

Return(dashed line,open arrow)

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Creation and Destruction

sdPlaceOrder

:CustomerWIndow

:CustomerChange<<create>>

getRating()

<<destroy>>

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In Class: Weblog Content Management System (CMS)

• (Pairs) Draw a sequence diagram for creating a new blog account.

The content management system allows an administrator to create a new blog account, provided the personal details of the new blogger are verified using the author credential database. A summary of the new blog account’s details should be mailed to the author.

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