# Sequence diagram example

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## Sequence diagram example

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Slide1

Sequence diagram example

T120B029

P7

2012 pavasaris

Slide2

What is the purpose of sequence diagram ?

The sequence diagram is used primarily to show the

interactions between objects

in the sequential order that those interactions occur.

Developers think sequence diagrams were meant exclusively for them

:-)

Business staff can find sequence diagrams useful to communicate how the business currently works by showing how various

.

A business-level sequence diagram can be used as a

requirements document

.

During the requirements phase use cases are often refined into

one or more sequence diagrams

.

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Sequence vs. Activity?

Little bit later…

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Notation 1/

An empty frameLifeline

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Notation 2

Sending a message/methos to another objectThe name is placed above the arrowed lineAnd represents an operation/method that the receiving object's class implements.

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Notation 3

Return messages – optionalThe use of return messages depends on the level of detail/abstractionReturn value is placed above dotted line

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Notation 4

Sending a message to itselfthe model draws attention to the fact that this processing takes place in the system object.

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Notation 5

Asynchronous message

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Notation 6

Who will guard the guardians themselves?Who will guard the guardians themselves

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Combined fragments (alternatives, options, and loops)

A combined fragment is used to group sets of messages together to show

conditional flow

in a sequence diagram.

Alternatives - classic "if then else" logic

Options - a simple "if then" without “else”

Loops – a repetitive sequence

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Alternatives

mutually exclusive choice between messages

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Option

used to model a sequence that, given a certain condition, will occur; otherwise, the sequence does not occur.

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Loops

does not require guard condition be placed on ita guard can have two special conditionsMinint = 1, Maxint = 5

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Breaks

most commonly used to model exception handlingcause the exiting of an enclosing interaction's sequence. In cases where a break is part of combined fragment, then only that fragment is exited.

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Nested diagrams

Referencing another sequence diagram

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SD mainly represent

step by step

ordered in time interaction between different objects.

AD also repersents an object role in workflow but level of repersenation is not dynamic like SD.

Example: Object lifeline and detailed sequence of interaction

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Online bookshop example

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Facebook user authentication in a Web application

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