Sequence Diagram

SEQUENCE DIAGRAMPrepared by: T. Fatimah Alageel

UML diagrams There are many ways of organizing the UML diagrams. Can be organized as the fallowing:

1. Structural diagrams: to show the building blocks of your system—features that don’t

change with time. Ex: Class diagram

2. Behavioral diagrams: to show how your system responds to requests or otherwise evolves

over time. Ex: Use case diagram

3. Interaction diagrams: Is a type of behavioral diagram. to depict the exchange of messages within a collaboration (a group

of cooperating objects). Ex: Sequence diagram & Collaboration diagram

Interaction Diagrams A series of diagrams describing the dynamic

behavior of an object-oriented system. A set of messages exchanged among a set of

objects within a context to accomplish a purpose.

Often used to model the way a use case is realized through a sequence of messages between objects.

The purpose of Interaction diagrams is to:– Model interactions between objects– Assist in understanding how a system (a use case) actually works– Verify that a use case description can be supported by the existing classes– Identify responsibilities/operations and assign them to classes

Interaction Diagrams UML

Collaboration Diagrams Emphasizes structural relations between

objects Sequence Diagram

The subject of this lecture

Sequence Diagrams Illustrates how objects interacts with

each other. Emphasizes time ordering of messages. Can model simple sequential flow,

branching, iteration, recursion and concurrency.

UML sequence diagrams Used during requirements

analysis To refine use case

descriptions to find additional

objects (“participating objects”)

Used during system design to refine subsystem

interfaces Classes are represented by

columns Messages are represented

by arrows Activations are

represented by narrow rectangles

Lifelines are represented by dashed lines

selectZone()

pickupChange()

pickUpTicket()

insertCoins()

Passenger TicketMachine

Nested messages

The source of an arrow indicates the activation which sent the message

An activation is as long as all nested activations Horizontal dashed arrows indicate data flow Vertical dashed lines indicate lifelines

selectZone()

Passenger Zone Selection F. TarifSchedule Display

lookupPrice(selection)

displayPrice(price)price

Dataflow

…to be continued...

Iteration & condition

Iteration is denoted by a * preceding the message name Condition is denoted by boolean expression in [ ] before the message

name

Passenger ChangeProcessor

insertChange(coin)

CoinIdentifier Display CoinDrop

displayPrice ( billed Amount)

lookupCoin(coin)

price

[billed Amount<0] returnChange(-billedAmount)

Iteration

Condition…to be continued...

…continued from previous slide...

*

Creation and destruction

Creation is denoted by a message arrow pointing to the object. Destruction is denoted by an X mark at the end of the destruction

activation. In garbage collection environments, destruction can be used to denote

the end of the useful life of an object.

PassengerChangeProcessor

…continued from previous slide...

Ticket

createTicket(selection)

free()

Creation

Destruction

print()

Software Design (UML)

Sequence Diagram

An object in a sequence diagram is renderedas a box with a dashed line descending from it.The line is called the object lifeline, and it represents the existence of an object over a period of time.

an Order Line


Sequence Diagraman Order Line a Stock Item

[check = “true”] remove()

check()

Messages are rendered as horizontalarrows being passed from object toobject as time advances down theobject lifelines. Conditions ( such as[check = “true”] ) indicate when amessage gets passed.


Sequence Diagraman Order Line a Stock Item

[check = “true”] remove()

check() Notice that the bottom arrow is different. The arrow head is not solid, and there is no accompanying message.

This arrow indicates a return from a previous message, not a new message.


Sequence Diagraman Order a Order Line

* prepare() An iteration marker, such as * (as shown), or *[i = 1..n] , indicates that a message will be repeated as indicated.

Iterationmarker


an Order Entrywindow an Order an Order Line a Stock Item

A ReorderItem

A DeliveryItem

new

[check = “true”] new

[needsToReorder = “true”]

needsToReorder()[check = “true”] remove()

check()* prepare()

prepare()

Object

Message

IterationReturn

Creation

Condition

Self-Delegation

[Fowler,97]

Basic Elements of a Sequence Diagram

Active Objects Actors or Objects Notated using the UML notation for class

instances “Life line” appears below active objects to

indicate their lifespan Messages

Arrowed lines that indicated communication between objects

Three Active Objects with Two Messages

Chessboard Database

Chess Player

make moverecord move

critique

Message Types Synchronous message (wait for return)

Return messages (response to previous message)

Asynchronous messages (no wait)

Flat (unspecified synchronization)

Note closed arrowhead

Creating/Deleting Objects Send messages <<create>> and <<destroys>>

Chessboard

Database<<create>>

critique<<destroys>>

Conditional MessagesChessboard

Database<<create>>

critique[unfavorable critique] <<destroys>>

Branching

Chessboard Database

Chess Player

[make move]

critique

[resign]

Alternative FlowChessboard Database

Chess Player

[make move]

[game over]

Control Rectangles Show when an object is involved in a sequence of messages

Chessboard ChessEngine

Request Position

Request Evaluation

Database

Record Data

Modeling Time Chess Client Chess Server

Send Player’s Move

Send Opponent’s Move

Diagonal message lines indicate that the messages take time to transmit

Specifying a Time Constraint on a message

Chess Client Chess Server



{sendTime for player’s move<2 seconds}

Modeling Loops




*[while !gameOver]

Modeling RecursionApplication Sorter

Sort List

Sort List

Arguments and Return Values

Web Interface

Database

GPA = RequestGPA(studentName)

Adding Notes to Diagrams




Send a move and get a move. If connection is lost, an automatic reconnect is attempted.

System Diagram notation

class instance named instance

:Sale s1:SaleSale

Which would you expect to find most often in a sequence diagrams?

Sequence Diagram Notation

: Register : Sale

doA

doB

doX

doC

doD

typical sychronous message shown with a filled-arrow line

a found message whose sender will not be specified

execution specification bar indicates focus of control

Figure 15.7

What does vertical placement communicate?

: Register : Sale

makePayment(cashTendered)

: Paymentcreate(cashTendered)

authorize

note that newly created objects are placed at their creation "height"

Figure 15.10

Documents

Sequence Diagram