ZEIT2301Design of Information Systems

Interaction Design: Sequence Diagrams

School of Engineering and Information TechnologyUNSW@ADFA

Dr Kathryn Merrick

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Topic 07: Interaction Design

Objectives To discuss the role of interaction diagrams in IS development.

To understand the notation, rules and style guidelines for creating interaction diagrams:

Today we will look at sequence diagrams Tomorrow we will look at communication diagrams

Reference: Text Ch 7

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Interaction Diagrams

Sequence and communication diagrams represent how objects collaborate to support business processes portrayed by use cases

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Sequence Diagrams

Sequence diagrams illustrate the objects that participate in a Use Case

Show the messages that pass between objects over time for a particular Use Case

Typically one sequence diagram is produced for each scenario in a use case may sometimes produce a sequence diagram showing all possible

scenarios.

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Sequence Diagrams

Elements of a sequence diagram:

Actors & Objects

Lifeline – represents time passing

Sometimes an object creates a temporary object - an “X” is placed at the point in the lifeline that the object is destroyed, e.g. shopping cart.

Execution occurrence – overlaid onto an object’s lifeline to show when the object is activated

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Sequence Diagrams

Elements of a sequence diagram (continued): Message – a communication between objects.

Types (used in sequence diagrams): Operation call message Return message Note: unless a return message

adds information, it should be omitted

Sequence – order of messages is top to bottom

Conditions [ ] – message is sent only if condition is true, e.g. [aPatient Exists] LookupBills () where “aPatient” represents an object of the Class Patient

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Sequence Diagram: Notation

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Sequence Diagram: Notation

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Sequence Diagram Example

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Sequence Diagram - Rent Movie

find customer()search (string)

search (string)

add(Cust, item)

enter movie()

rent (movie)

printInvoice() generateRentalTotal()

Object

Lifeline

ActivationMessage

:CheckoutMgr :Inventory:Customer :RentedItems:Employee

The notation “:Inventory” means an anonymous object of class Inventory.

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Sequence Diagram: Places Order Use case

These “temporary” objects can now cease to exist

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Sequence Diagrams versus Class Diagrams

The messages identified in your Sequence Diagram, then become operations in the Class Diagram.

If the aCustomer:Customer object sends a message “createSR()” to the aSR:SearchRequest object then the class SearchRequest should have an operation createSR()

Note that the requested operation belongs to the recipient of the message.

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Customer

studentIDname

updateAddress(). . . . .

Sequence Diagram and Class Diagram Example

searchRequest

searchNosearchTerm. . . . .

createSR() . . . .

1..1 0..*

requests

Message from Sequence Diagram becomes an operation in the Class Diagram. Operation belongs with the recipient of the message.

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Summary

After today’s lecture you should be able to:

Construct sequence diagrams

Use sequence diagrams to inform the design of class diagrams