© 2008 Prentice Hall, Ovidiu NoranLecture 7b 1

Lecture 7b

Modelling OO Logic Requirements: Sequence Diagrams and Activity

Diagrams

(Textbook Chapter 8, Appendix)

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 2

Learning Objectives

Understand how to detail use cases and represent some system logic with sequence diagrams.

Understand how to represent processes and system logic with activity diagrams.

Understand the relationship between different types of diagrams

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 3

Interaction and Activity Diagrams

Use Case diagrams are too simple to show details of the interactions among objects within a use case.

In addition to written use cases, Interaction Diagrams (Sequence and Collaboration) are used to detail the interactions taking place in a use case

Activity Diagrams are used to show the conditional logic for the sequence of system activities needed to accomplish a business process.

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 4

Dynamic Modelling: Sequence Diagrams

Sequence diagram: depicts the interactions among objects during a certain period of time.

May be presented either in a generic form or in an instance form.

Generic form shows all possible sequences of interactions, corresponding to all the scenarios of a use case.

Instance form shows the sequence for only one scenario (a specific combination of conditions within a use case (Fowler, 2000))

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Elements of a sequence diagram Objects: represented by boxes at top of

diagram. Lifeline: the time during which an object

exists. Messages: means by which objects

communicate with each other. Objects (derived out of classes) and

messages are essential elements of the OO approach. More in future lectures…

Sequence Diagrams (Cont.)

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Activation: the time period during which an object performs an operation.

Synchronous message: a type of message in which the caller has to wait for the receiving object to finish executing the called operation before it can resume execution itself.

Sequence Diagrams (Cont.)

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Simple message: a message that transfer control from the sender to the recipient without describing the details of the communication.

Asynchronous message: a message in which the sender does not have to wait for the recipient to handle the message.

Sequence Diagrams (Cont.)

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Scenario modelled: Class registration. Assumptions: course has no prerequisites

1. Registration Clerk opens the registration window and enters the registration information

2. Check if the class is open

3. If the class is open, check if the course has any prerequisites.

4. Assumed course has no prerequisites. Register the student for the class; increment the class size by one.

5. Check if the class ifs full; if not, do nothing

6. Display the confirmed registration in the registration window

Sequence Diagrams (Cont.)

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 9Sequence diagram for a class registration scenario without prerequisites

ObjectName:ClassName ‘Non-persistent’

(control) object

Lifeline

No response shown. (assumption: class open)

Guard conditions

‘Self delegation’ (call upon one’s own operation(s)

(Object destroys itself)

Activation (performs operation) Synchronous

message(all shown are synchronous)

AnonymousObject

Named Object (‘a New Registration’)

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Scenario modelled: Class registration. Assumptions: course has prerequisites, class not full

1. Registration Clerk opens the registration window and enters the registration information

2. Check if the class is open

3. If the class is open, check if the course has any prerequisites. Assumed course has prerequisites.

4. If the student has taken the prerequisites, then register the student for the class and increment the class size by one.

5. Check if the class ifs full; assumed class not full.

6. Display the confirmed registration in the registration window

Sequence Diagrams (Cont.)

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 11Sequence diagram for a class registration scenario with prerequisites

Guard condition for existing prerequisites

In this scenario, assume class not full

Time

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 12A sequence diagram for “Prerequisite Courses Not Completed” use case

Student has not taken prerequisites

Scenario:

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Process Modelling: Activity Diagrams

Elements of Activity Diagrams: Activity: a behavior that an object carries

out while in a particular state. Transition: a movement from one activity

or state to another. Branch: a diamond symbol containing a

condition whose results provide transitions to different paths of activities.

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Activity Diagram for a Customer Order Process

Time

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Process Modelling: Activity Diagrams (Cont.)

Synchronization bar: horizontal or vertical bars denoting parallel or concurrent paths of activities. Fork: the beginning of parallel activities. Join: the end of parallel activities.

Swimlanes: columns representing different organisational units of the system.

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Process Modelling: Activity Diags (Cont.)

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Process Modelling: Activity Diags (Cont.)

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 18 Hospital Pharmacy Level-0 DFD

2.0

Review Prescription

Order by Station

3.0

Fill Order

4.0

Generate Label

Nurses Station

Doctor

Billing Dept

D1

Patient File

Prescription

Unfilled Order Info

Unfilled Order

Info Response

Order Info

Patient Number

and Drug Type,

Amount & Cost

PharmacyTech ReviewPrescription

Prescription

Ord

er F

ill In

fo

1.0

Review & Send

Prescription to Station

Drug Label Info

Drug Label Info

Patie

nt In

fo

Comparing Activity Diagrams with DFDs

Processes are shown in both diagrams. HOWEVER…

-No time dimension, hence no synchronisation, etc features-No explicit decision logic (remember how it can besuggested in DFDs ??

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Relationship of OO techniques / diagrams

Source: (Satzinger et. al, 2008)

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Summary In this appendix you had the

opportunity to learn how to: Understand how to detail use cases and

represent some system logic with sequence diagrams.

Understand how to represent system logic with activity diagrams.

Understand the relationship between different types of diagrams

© 2008 Prentice Hall, Ovidiu NoranLecture 7b 21

References Fowler, M. 2000. UML Distilled: A Brief

Guide to the Object Modelling Language. 2nd Ed. Reading, MA: Addison Wesley

Satzinger, G., Jackson, R.Burd, S. 2008. Systems Analysis and Design in a Changing World. 5th Ed. Course Technology