1. ZEIT2301 Design of Information Systems
Topic 02: Project Initiation
ZEIT2301 Design of Information Systems Interaction Design: Sequence Diagrams
School of Engineering and Information Technology
Dr Kathryn Merrick
Session 2, 2010

2. Topic 07: Interaction Design
ZEIT2301 Design of Information Systems
Topic 02: Project Initiation
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
Session 2, 2010

3. Interaction Diagrams
Sequence and communication diagrams represent how objects collaborate to support business processes portrayed by use cases 3

4. 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. 4

5. 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 5

6. Sequence Diagrams Operation call message
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 6

7. Sequence Diagram: Notation7

8. Sequence Diagram: Notation8

9. Sequence Diagram Example
Session 2, 2010 9

10. Sequence Diagram - Rent Movie
:CheckoutMgr
:Customer
:Inventory
:RentedItems
:Employee
find customer()
search (string)
Object
enter movie()
search (string)
Message
Activation
rent (movie)
add(Cust, item)
Lifeline
A Sequence Diagram Example
printInvoice()
generateRentalTotal()
Depicts how the classes within the system work together. The objects at the top represent class roles. The dashed lines that extend from each object represent lifelines. The thin rectangles on the lifelines represent activations. The horizontal arrows between lifelines indicate the messages exchanged between objects. The horizontal arrows are labeled with the message that is sent between the class roles. The message triggers an operation in the receiving object.
The objects defined inside the rectangle can be defined in one of the three ways:
The object name, the object name and its class, or just the class name (anonymous object)
The notation “:Inventory” means an anonymous object of class Inventory.
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11. Sequence Diagram: Places Order Use case
Session 2, 2010 11
These “temporary” objects can now cease to exist

12. 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. 12

13. Sequence Diagram and Class Diagram Example
searchRequest
Customer
requests
searchNo
searchTerm
studentID
name
1..1
0..*
updateAddress()
createSR()
Message from Sequence Diagram becomes an operation in the Class Diagram. Operation belongs with the recipient of the message.
Session 2, 2010 13

14. ZEIT2301 Design of Information Systems
Topic 02: Project Initiation
Summary
After today’s lecture you should be able to:
Construct sequence diagrams
Use sequence diagrams to inform the design of class diagrams
Session 2, 2010