Use Cases

Yonglei Tao

Typical Commercial Applications 300-600 entries in model dictionary 20-100 use cases 5-20 activities per use case 100-500 domain classes 1 to 12 operations per class

3

AcquiringRequirements

Software architecture

Use Cases

Deriving Use Cases from Requirements

Allocating Use Cases & Subsystemsto Iterations

Business goals& needs

Current situation

Preliminary requirements

Abstract & high level use cases, use case diagrams

Use case-iteration allocation matrix

(a) Planning Phase (b) Iterative Phase – activities during each iteration

Actor-System Interaction Modeling

Domain Modeling

AccommodatingRequirements Change

Behavior Modeling &Responsibility Assignment

Deriving Design ClassDiagram

Test Driven Development, Integration, & Deployment

Customer feedback

Iteration use cases

Domain model

Expanded use cases & UI design

Behavior models

Design class diagram

Domain model

Use case-iteration allocation matrix

Producing an Architecture Design

4

A Use Case Diagram

Checkout Document

Return Document

Search for Document

Library System

Patron

5

Simplify with Use of Inheritance

Startup

Shutdown

Admin

Library System

Checkout a Document

Patron Return a Document

6

Simplify with Use of Inheritance

Login

Logout

SAMS/Search Program

SAMSEnd User

SAMSAdmin

SAMSStaff

This is OK. Login

Logout

SAMS/Search Program

SAMSEnd User

SAMSAdmin

SAMSStaff Better

7

Are These Use Cases? Why? Check authorization / check authentication Enter a password Process data Open a file Click on a menu item Traverse a linked list. Start a system

8

Use Case Diagram – Overly Complex

Log In

Log Out

Start Up

SAMS

SAMSEnd User

SAMSStaff User

SAMSAdmin

Add Program

Delete Program

Edit Program

Create User

Delete User

Update User

Search for Programs

Display ProgramDetail

Apply OnlineShutdown

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Create User

Delete User

Update User

SAMS/User Mgmt

SAMSAdmin

Add Program

Delete Program

Edit Program

SAMS/Program Mgmt

SAMSStaff

Search for Programs

Display ProgramDetail

Apply Online

SAMS/End User

SAMSEnd User

Start Up

Shutdown

Login

Logout

SAMS/Authentication

SAMSEnd User

SAMSAdmin

SAMSStaff

Software engineeringprinciple applied:• separation of concerns• divide and conquer

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Verify the Use Cases Identified Ask questions about each use case:

(1) Is it a business process? (2) Is it initiated by an actor? (3) Does it end with the actor? (4) Does it accomplish something useful for

the actor? All the answers to above questions must

be “yes”

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Example: Library System Requirements of a library system:

R1. The library system must allow a

patron to

check out documents.

R2. The library system must allow a

patron to

return documents.

use case actorsystem

Use CaseBusiness Process?

Begin w/ Actor?

End w/ Actor?

Useful Task for Actor?

Use Case? Actor System

R1 Checkout Document Y Y Y Y Y Patron Library

System

R2 Return Document Y Y Y Y Y Patron Library

System

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Example: Oversea Exchange ProgramR1. The web-based application must provide a

search capability for overseas exchange programs using a variety of search criteria.

R2. The web site must provide a hierarchical display of the search results to facilitate user navigation from a high level summary to details about an overseas exchange program.

SystemActorUse

Case?

Useful Task for

Actor?End w/ Actor?

Begin w/

Actor?

Business

Process?Use Case

R1 Search for Programs Y Y Y Y Y User Web

App.

R2 Display Program Details

Y Y Y Y Y User Web App.

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Requirements Use Case Tractability Will the system satisfy all the

requirements? Are any use case missing? Are any use case not needed? Which requirements are more important

than the other? Which use cases should the developer

focus on timely delivery?

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Requirements-Use Case Traceability Matrix

R1

R2

R3

R4

R5

R6

UC1 UC2 UC3 UC4 UC5 UC6PriorityWeight

Score

3

2

2

1

1

1

X

X

X

X

X

XX

X

X

5 5

X

1 1 3 1

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Project Planning by Use Cases

1) Identify dependencies between the use cases: use cases are business processes business processes depend on each other

2) Compute a partial order to develop the use cases according to the dependencies.

3) Schedule the development according to the partial order begin with higher priority use cases (risky,

high-value, architecturally significant, and executable)

time-boxed iterations

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Project Planning with Use Cases

A planning tool to let the development team know• which use cases to be developed by what time• which use cases are ready for integration and system testing• what is the status or configuration of the project

1 2 3 4 5 6 7 8 9 10 11 12UC1UC2

UC3

UC4UC5

UC6

UC7

UC29UC30

X

X

X X

X

X

X

X

X

.

.

.

.

.

.

XX

17

Actor-System Interaction Modeling Specify how the system interacts with the

actors to carry out the use cases. to identify what is expected from the system

In an expanded use case

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Actor: Caller System: Telco1.the caller picks up the handset from the phone base.

2. the system generates a dial tone.

3. the caller dials each digit of the phone number.

4. the system responds with a DTMF tone for each digit dialed.

5. the caller finishes dialing.

6. he system produces the ring tone.

7. the caller hears the ring tone.

Expanded Use Case – Initiate a Call

system response

actor input &actor action

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Domain Model and Use Cases

Part of Domain Model

Programnametypedepartmentinstitutionsubjectregioncountrylanguageterm

Student

Staff

Application

student_nametermyearlanguagedate_appliedstatus

manage

1..** *

1..**

withname, type, department, ...

20

Expanded Use Case – Add Program

Actor: Staff User System: SAMS

0. System displays the staff main page.1. TUCBW the staff user clicks the “Add Program” button.

2. System displays the Add Program page.3. The staff user enters

program detail and clicks the ”submit" button.

4. System checks the submitted info and shows a confirmation message if no error is found.

5. TUCEW the staff user clicks the “OK” button on the confirmation page.

Precondition: Staff User has logged into System and Staff Main Page is shown

Postcondition: The added program is immediately available for search.

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Showing User Interface Prototypes Showing user interface prototypes with

expanded use case specification is extremely useful to obtain user feedback early in the lifecycle.

These user interface prototypes may be reused in the preparation of the user’s manual, which can take place concurrently with the development effort.

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(7) TUCEW staff member is shown a message that the program has been successfully added.

(6) The System updates the database with the new program details and displays a success message.

(5) User fills the form and clicks on submit button.

(4) System shows the Add Program Form

(3) Staff member clicks on Add Program link.

(2) System shows the submenu consisting of various operations that a staff user can do under Program Management.

(1) TUCBW staff member clicks on Program Management link on welcome page.

System : SAMSActor : Staff User

Showing UI Prototypes w/ Expanded Use Case

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Video Store Use Case DiagramVideo Store

Information System

Administrator

ManageInventory

ManageMemberships

Clerk

Customer

«actor»Credit

AuthorizationService

Pay Fines

Rent Items

Log In

Manage Users

Banking System Use Case Diagram

Validate PIN Use Case

Withdraw Funds Use Case

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Class ExerciseWhat are the use cases for the Vending

Machine?

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Class Exercise: The Vending Machine

The Vending Machine has a display, an alphanumeric keypad, a coin insertion slot, and an item dispenser. The display shows the vending items like chocolates, candies, potato chips, Coke, sprite, etc. Each type of item has a price and a label consisting of a letter A, B, C, ... and a digit 1, 2, ... A customer inserts coins through the coin slot. Each time a coin is inserted an LCD displays the total amount. The customer can press a letter and a digit to enter his selection after enough coins have been inserted. If the total amount is greater than or equals to the item selected, the vending machine dispenses the item and returns the change to the customer. A customer can change his mind and request that the coins be returned by pressing the return button.