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UML Sequence Models

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Specifying behavior using the UML

� Class models describe objects and their relationships� Behavior can be specified in terms of operation pre and

postconditions, but behavior is not the primary focus of a class model

� Behavioral models in the UML� State models: describe control aspects of a system –

provides descriptions sequences of operations without regard for what the operation do.

� Interaction models: describe interactions among objects� Activity models: description of a behavioral feature

expressed in terms of sequences of steps.

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How things happen in the UML

� An action is executed by an object� May change the contents of one or more variables or slots

� If it is a communication (“messaging”) action, it may:

� Invoke an operation on another object

� Send a signal to another object

� Either one will eventually cause the execution of a procedure onthe target object…

� …which will cause other actions to be executed, etc.

� Successor actions are executed

� Determined either by control flow or data flow

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Sequence Models

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Overview

� Realizations of use cases can be expressed as interaction diagrams� Objects interact to accomplish use case goals.

� Object interactions are described in terms of messages sent among objects

� Sequence diagrams allow one to view only the parts of a system involved in accomplishing use case goals

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Sequence Diagram: Basic constructs

name : Classobject symbol

lifeline

activation

other

stimulus

name (…)

return

: Class

create

new (…)

delete

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Different kinds of arrows

Synchronous message: Operation call

Asynchronous message

Return

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Example: different arrows

caller exchange callee

Asynchronous Flow

lift receiver

dial tone

dial digit

dial digit

ringing tone ringing signal

lift receiver

teller : Order : Article

Synchronous Flow

getValue

price

getName

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sd GoHomeSetup

:ServiceUser:ServiceBase

ref SB_GoHomeSetup:ServiceTerminal

opt

ref FindLocation

SetHome

SetInvocationTime

SetTransportPreferences

refAuthorization

A more complex Sequence Diagram

(UML 2.0)Frame and Name

Lifeline is an object

Interaction Occurrence

Combined Fragment

Plain asynchronous message

sd Authorization

:ServiceUser:ServiceBase

ref SB_Authorization:ServiceTerminal

Code

OK

OnWeb

OK

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Combined fragment types� Alternatives (alt)

� choice of behaviors – at most one will execute� depends on the value of the guard (“else” guard supported)

� Option (opt)� Special case of alternative

� Loop (loop)� Optional guard: [<min>, <max>, <Boolean-expression>]� No guard means no specified limit

� Break (break)� Represents an alternative that is executed instead of the

remainder of the fragment (like a break in a loop)� Parallel (par)

� Concurrent (interleaved) sub-scenarios� Negative (neg)

� Identifies sequences that must not occur

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Combined fragments and data

:ServiceUser :ServiceBase :ServiceTerminal

sd GoHomeInvocation(Time invoc)

:Clock

InvocationTime FindLocation

TransportSchedule

loop

alt

ScheduleIntervalElapsedFindLocation

TransportSchedule

GetTransportSchedule

TransportSchedule

FetchSchedule

[Now>interv+last]

[pos-lastpos>dist]

[Now>invoc]loop

Choice

Operand Separator

Guarding InteractionOperand with an InteractionConstraint

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Exampe: A Problem

� [Variation of a program example used in the book “Refactoring” by Martin Fowler]

� Program calculates and prints a statement of a customer’s charges at a video store. There are three types of movies: Regular, NewRelease, Children.

� Rates� Regular: 2.00 for 2 days; late 1.50/late day� Children: 1.50 for 3 days; late 1.50/late day� NewRelease: 3.00/day

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Design 1: Class DiagramCustomer

Rental Movie

makes

refers_to

_rentals

_movie

1

*

*

1

name: String

addRental()getName()statement()- getAmount()

daysrented:int

getDaysRented()getMovie()

title:StringpriceCode:int

getPriceCode()setPriceCode()getTitle()

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Design 1: Sequence Model

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Design 1: Code for MoviePublic class Movie{

public static final int CHILDREN = 2;public static final int REGULAR = 0;public static final int NEW = 1;

private string _title;private int _priceCode;

public Movie (String title, int priceCode){_title = title; _priceCode=priceCode;}

public int getPriceCode(){return _priceCode;}

public int getTitle(){return _title;}

public void setPriceCode(int arg){_priceCode=arg;}

}

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Code for Rental

class Rental{

private Movie _movie;

private int _daysRented;

public Rental (Movie movie, int daysRented){

_movie=movie; _daysRented=daysRented;}

public int getDaysRented(){

return _daysRented;}

public Movie getMovie(){

return _movie;}

}

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Code for Customerclass Customer{

private string _name;

private vector _rentals = new Vector();

public Customer (String name){_name = name;}

public void addRental(Rental arg){

_rentals.addElement(arg);}

public String getName(){

return _name;}

public String statement(){…}

}

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Code Skeleton for statement()

Derived from Sequence Model

public String Statement (){Enumeration rentals = _rentals.elements();

\…

while(rentals.hasMoreElements()){

\\...Rental R =(Rental)rentals.nextElement();

\\

Movie M=aRental.getMovie();

int PC=M.getPriceCode();String T = M.getTitle();

int days=R.getDaysRented(); }

\\…

}

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Code for statement()public String Statement (){

double totalAmt = 0;

Enumeration rentals = _rentals.elements();

String result = “Record for”+getName()+”\n”;

while(rentals.hasMoreElements()){Rental aRental=(Rental)rentals.nextElement();

thisAmt=getAmount(aRental);

String t=aRental.getMovie().getTitle();

result += ”\t”+ t + String.valueOf(thisAmt)+”\n”;totalAmt=totalAmt+thisAmt;

}

result+=”Amount owed is”+String.valueOf(totalAmt)+” \n”;

return result;}

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Code for getAmount()Private double getAmount (Rental aRental){

Movie aMovie=aRental.getMovie();

int pc=aMovie.getPriceCode();

int days=aRental.getDaysRented();int thisAmt = 0;

switch (pc){

case Movie.REGULAR:

thisAmt = 2;

if (days > 2)

thisAmt += (days-2)*1.5;

break;

case Movie.NEW:thisAmt = days*3;

break;

case Movie.CHILDREN:

thisAmt = 1.5;

if (days > 3)

thisAmt += (days-3)*1.5;

break;

}return thisAmt;

}

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Design 2 Sequence Model

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Design 2 Class Diagram

Customer

Rental Movie

makes

refers_to

_rentals

_movie

1

*

*

1

name: String

addRental()getName()statement()getTotalCharge()

daysRented:int

getDaysRented()getMovie()getCharge()

title:StringpriceCode:int

getPriceCode()setPriceCode()getTitle()

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Design 3: Class Diagram

Rental Movie

makes

refers_to

_rentals

_movie

1

*

*

1

Customer

name: String

addRental()getName()statement()getTotalCharge()

daysRented:int

getDaysRented()getMovie()getCharge()

title:String

getCharge()getTitle()

Price

getCharge(days)

NewRelPrice

getCharge(days)

ChildrenPrice

getCharge(days)

RegularPrice

getCharge(days)

1

*

has_state

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Design 3: Sequence Model

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sdsd ATMATM--transactiontransaction

client: atm: dbase:

Referencing interaction diagrams

insertCard

CheckPinref

alt [chk= OK]

[else]error(badPIN)

DoTransactionref

sdsd CheckPinCheckPin

client: atm: dbase:

askForPIN

data(PIN)check(PIN)

result(chk)result(chk)

Interaction Frame Lifeline is one

object or a part

Lifeline is one

object or a part

Interaction OccurrenceInteraction Occurrence

Combined (in-line)

Fragment

Combined (in-line)

Fragment

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Creating Interaction Model

� Set interaction context� Use Case scenario

� Identify (controller) object responsible for handling the event initiating the interaction

� Identify objects that collaborate with the controller (collaborators).

� Specify message passing sequence that handles the initiating message.

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Interaction modeling tips

� Set the context for the interaction.� Include only those attributes of the objects that are relevant.� Express the flow from left to right and from top to bottom.� Put active objects to the left/top and passive ones to the

right/bottom.� Use sequence diagrams

� to show the explicit ordering between the stimuli

� when modeling real-time