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Fall 2002 SJSU -- CmpE

Object-Oriented Analysis & Design

Dr. M.E. Fayad, Professor

Computer Engineering Department ± RM#

College of Engineering

San José State University

One Washington Square

San José, CA 95192-0180

URL: http://www.cmpe.sjsu.edu/~fayad

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L09-S2 Use Case ModelingFall 2002 SJSU ± CmpE M.E. Fayad

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Lesson 12:Use Case Modeling

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Lesson Objectives

Objectives

3

Overview of Previous Lecture

Discuss the following:

± What is use case modeling?

± Use Case Modeling -- Core concepts

± Use Case Diagram tour

± When to model use cases

±Use Case Modeling tips

± Examples: Library & Univer sity Registration

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What is use case modeling?

use case model: a view of a system

that emphasizes the behavior as it appear s to outside user s. A use case

model partitions system functionality

into transactions (µuse cases¶) that

are meaningful to user s (µactor s¶).

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Use Case Modeling: Core ElementsConstr uct Description Syntax

use case A sequence of actions, includingvariants, that a system (or other entity) can perform, interacting with

actors of the system.actor A coherent set of roles that users

of use cases play when interactingwith these use cases.

systemboundary

Represents the boundary betweenthe physical system and the actorswho interact with the physicalsystem.

UseCaseName

ct ¡ r Name

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Constr uct Description Syntax

association The participation of an actor in a usecase. i.e., instance of an actor andinstances of a use case communicatewith each other.

extend A relationship from an extension usecase to a base use case, specifyinghow the behavior for the extensionuse case can be inserted into thebehavior defined for the base usecase.

generalization A taxonomic relationship between amore general use case and a morespecific use case.

Use Case Modeling: Core Relationships

<<extend>>

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Constr uct Description Syntax

include An relationship from a base use caseto an inclusion use case, specifyinghow the behavior for the inclusion usecase is inserted into the behavior defined for the base use case.

Use Case Modeling: Core Relationships (cont¶d)

<<include>>

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Shows use cases, actor and their

relationships Use case internals can be specif ied by

text and/or interaction diagrams Kinds

± use case diagram

± use case description

Use Case Diagram Tour

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Fig. 3-44, UML N otation Guide

C u s tom er

Su pe rv i so r

S al es pe r so nPlac e

E s t a b l i s hc r ed i t

C h e c k

T el ep h o n e C a t a l o g

Fi l l o r d e r s

S h i p p in g C l e r k

s t a t u s

o r de r

Use Case Model

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Use Case Diagram: Relationships

additional requests :

Order Product

SupplyArrange

«include»«include»«include»

RequestCatalog

«extend»Extension points

PaymentCustomer Data

after creation of the order

Place Order

1 * the salesperson asks for the catalog

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Use Case Diagram: Actor Relationships

E tablis

C dit

Place

Or der

Salesper so

Supervisor

1 *

1 *

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Use Case Description: Change FlightActor s: traveler, client account db, airline reservation system

Preconditions:

y Traveler has logged on to the system and selected µchangeflight itinerary¶ option

Basic cour se

y System retrieves traveler¶s account and flight itinerary fromclient account database

y System asks traveler to select itinerary segment she wants tochange; traveler selects itinerary segment.

y System asks traveler for new departure and destinationinformation; traveler provides information.

y If flights are available theny «

y System displays transaction summary.

Alternative cour ses

y If no flights are available then «

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When to model use cases

Model user requirements with use cases.

Model test scenarios with use cases.

If you are using a use-case driven method

± start with use cases and derive your structuraland behavioral models from it.

If you are not using a use-case driven method

± make sure that your use cases are consistentwith your structural and behavioral models.

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Use Case Modeling Tips

Make sure that each use case describes a signif icant chunk of

system usage that is under standable by both domain experts and

pr ogrammer s

When def ining use cases in text, use nouns and verbs accurately

and consistently to help derive objects and messages for

interaction diagrams

Factor out common usages that are required by multiple use cases

± If the usage is required use <<include>>

± If the base use case is complete and the usage may be optional,

consider use <<extend>>

A use case diagram should ± contain only use cases at the same level of abstraction

± include only actor s who are required

Large number s of use cases should be organized into packages

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Sample Problem Statement: Library System

You have been contracted to develop a

computer system for a univer sity library. The

library currently uses a 1960s pr ogram,written in an obsolete language, for some

simple bookkeeping tasks, and a car d index,

for user br owsing. You are asked to build an

interactive system which handles both of

these aspects online.*

*Example from: ³Using UML´, by: Pooley and Stevens

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First Step!

Time to start gathering the user requirements.

± Different users will have different, sometimes

conflicting priorities ± Users will not, necessarily know what they

want

± It is very possible to miss something vital

± The managers do not always know what theusers have to do

± Users can be, and frequently are, hostile.

Why? What can be done about it?16

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The Use Case Model

We must now identify the users of the system

and the tasks they must undertake with thesystem. The details of the use case should

be documented, using a Use Case Template.

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The Use Case Template

Use Case TemplatePACKAGE: _________________ [Description ( an over view of the package)].

USE CASES: [A package will have one or more U se C ases].

Use Case No.: [1.1 ]

Use Case Title: [A descriptive title]

[E x. adding a new patient, or adding a new role].

Actor s: _______ , _______ , _______ , _______ .

[Any users of the U se C ase, ex. human, machine, other systems or subsystems].

Corresponding Roles: _______ , _______ , _______ , _______ .

[T here is a different role per actor in every U se C ase].

Classes: _______ , _______ , _______ , _______ .

[ List all the classes within the U se C ase Description].

Enduring Business Themes (EBT): _______ , _______ , _______

Business Objects (BO): _______ , _______ , _______ , _______ .

Industrial Objects (IO): _______ , _______ , _______ , _______ .

[T his represents a clear classification of all the classes within the use case description].

Description of the Use Case:

[Describes the data flow and the logic flow of the U se C ase]. 18

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L09-S19 Use Case ModelingFall 2002 SJSU ± CmpE M.E. FayadCopyright© 1997 by Rational Software Corporation

Documenting Use Cases

A flow of events description is created for each use case

± Written from an actors point of view

Details what the system must provide to the actor whenthe use case is executed

Typical contents

± How the use case starts and ends

± ormal flow of events

± Alternate flow of events

± Exceptional flow of events

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Actors

An actor is someone or something that must interact with the

system under development

BookBorrower

Browser

Librarian

JournalBorrower

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Use Cases

Actors are examined to determine their needs

± BookBorrower

Checkout and return books

± Browser

locate and peruse items of interest

± Librarian

maintain order and accountablility

± JournalBorrower

checkout and return journals

Checkout JournalCheckout Book Return Book

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Use Case Description

The usual course through the system when actor is using the

system is called the basic course. Other courses would be

modeled as extending Use Cases.

An example of a basic course would be:

± Borr ow copy of book A BookBorrower presents a book. The

system checks that the potential borrower is a member of the

library, and that s/he does not already have the maximum

permitted number of books on loan. This maximum is six unless

the member is a staff member, in which case it is 12. If both

checks succeed, the system records that this library member has

this copy of the book on loan.**Example from: ³Using UML´, by: P ooley and Stevens 22

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Use Case Diagram for the first iteration


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What Requirements would an ideal system satisfy?

Books and Journals: The library contains books and

journals. It may have several copies of a given book. Some

of the books are for short term loans only. All other booksmay be borrowed by any library member for three weeks.

Only members of staff may borrow journals. Members of the

library can normally borrow up to six items at a time, but

members of staff may borrow up to 12 items at one time.

New books and journals arrive regularly, and are sometimesdisposed of. The current year¶s journals are sent away to be

bound into volumes at the end of each year.*


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What Requirements would an ideal system satisfy?

Borr owing: It is essential that the system keep track of

when books and journals are borrowed and returned, since

the current system already does that. The new system

should produce reminders when a book is overdue. Theremay in future be a requirement for users to be able to extend

the loan of a book if it is not reserved.

Br owsing: The system should allow users to search for a

book on a particular topic, by a particular author, etc., to

check whether a copy of the book is available for loan, and if not, to reserve the book. Anyone can browse in the library.*


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Use Cases for the library


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Copyright© 1997 by Rational Software Corporation

Actors

Student

Registrar

Professor

Billing System 28

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Use Cases

Actors are examined to determine their needs

± Registrar

maintain the curriculum

± Professor

request roster ± Student

maintain schedule

± Billing System

receive billing information from registration

Maintain ScheduleMaintain Curriculum Request Course Roster

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Maintain Curriculum: Flow of Events (description)

This use case begins when the Registrar logs onto the

Registration System and enter s his/her passwor d. The system

verif ies that the passwor d is valid (E-1) and pr ompts the

Registrar to select the current semester or a future semester (E-

2). The Registrar enter s the desired semester . The systempr ompts the pr of essor to select the desired activity: ADD,

DELETE, REVIEW, or QUIT.

If the activity selected is ADD, the S-1: Add a Cour se subflow is

per for med.

If the activity selected is DELETE, the S-2: Delete a Cour se

subflow is per for med. If the activity selected is REVIEW, the S-3: Review Curriculum

subflow is per for med.

If the activity selected is QUIT, the use case ends. 30

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Use Case Model

Use case diagrams are created to visualize the relationshipsbetween actor s and use cases

Student

Registrar

Professor

Maintain Schedule

Maintain Curriculum

Request Course Roster

Billing System

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Uses and Extends Use Case Relationships

As the use cases are documented, other use caserelationships may be discovered

± A uses relationship shows behavior that is common toone or more use cases

± An extends relationship shows optional behavior

Register for courses

<<uses>>

Logon validation<<uses>>

Maintain curriculum

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Possible Problems with Use Cases

1. Use Cases emphasize ordering. This can be

considered to be incompatible with object

technology.

2. Over modeling ± Leads to requirement inflation.

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Cautions

Do not invent requirements!

± Use cases are about the user¶s requirements,not about what you, as the designer might

think that the system could usefully do!

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Acknowledgements

Object Modeling with OMG UML:Introduction to UML

± Cris Kobryn

± Chief Scientist, InLine SoftwareCo-Chair UML Revision Task Force August 2000

³ Using UML: Software Engineering With Objects and

Components´

by: Rob Pooley and Perdita Stevens

³ Analysis and Design with UML´Copyright© 1997 by Rational Software Corporation

© 1999-2000 OMG and Tutorial Contributors: EDS, IBM, Enea Data, InLine Software,IntelliCorp, Kabira Technologies, Klasse Objecten, ObjectTime Ltd., Rational Software, Unisys

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Use Case No.: 1.1.1

Use Case Title: F ind C andidate

Actor s: Registrar Roles: Data Entry Clerk (Registrar),

Classes: IDSession, PersonProfile, PersonIdentifier, PersonTraits, CandidateListGenerator, DataManager

Enduring Business Themes: (EBT): identity, security,

Business Objects: IDSession, IDManager, DataManager,

PersonIdentifier Industrial Objects: CandidateList, PersonTraits, PersonProfiles,

SecurityManager, TraitGatekeeper

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Sample Use Case from Philips Project (1)

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1. The Registrar enters the information about a person into theSystem.

2. IDSession clears the request with Security.

3. The System tells the Person-Identifier to search for candidates.

4. The Person-Identifier gives the request to its DataManager

5. The DataManager determines a list of candidates, using itsCandidateListGenerator and its set of PersonProfiles and returns itto the System.

6. The Registrar chooses the candidate from the list thatrepresents the person.

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Use Case No.: 1.2.1

Use Case Title: R egister N ew I D

Actor s: Registrar Roles: Data Entry Clerk (Registrar),

Classes: IDSession, IDManager, PersonProfile, PersonTraits,CandidateList, PersonIdentifier

Enduring Business Themes (EBT): identity, security

Business Objects (BO): IDSession, IDManager , PersonIdentifier

Industrial Objects (IO): PersonProfile, PersonTraits, CandidateList

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1. The Registrar enters the information about a person into the IDSession.

2. The IDSession has security clear the request.

3. The IDSession has the PersonIdentifier search for candidates. 4. The Person-Identifier determines that no candidates fit the criteria.

5. The Person-Identifier gives this information to the system.

6. The informs the Registrar that no candidates exist.

7. System asks the Registrar if the person should be added as new.

8. Registrar tells System to add new person. 9. System sends traits to ID-Manager.

10. ID-Manager creates a new profile.

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Exceptional Flow of Events 01: If any of the identifying information

entered by the Registrar is incomplete or invalid the system displays

corresponding error message(s). The system will not validate the

New Person until all identifying information is made available.

Exceptional Flow of Events 02: In case the system determines that

one or more of the identifying information for a person matches one or

more person(s) already in the system the Registrar is displayed with a

screen listing all the person(s) meeting the search criteria. The

Registrar is then given the opportunity to either create the person inthe system with a new ID or pick one from the selection list.

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Use Case No.: 1.3.1

Use Case Title: Get Patient Profile using Patient ID

Actor s / Roles: Nurse, Patient, and Profile Access Classes:

Enduring Business Themes (EBT): Diagnosis, Customer Service

and Complete Medical History

Business Objects (BO): Profile Access, Identify Person and

Identity

Industrial Objects (IO): Identity Access

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1. The Nurse enters the Person ID for the person.

2. The Person Identification system determines the validity of thePerson ID.

3. The Get Profile System returns the profile the specified Person ID.

Exceptional Flow of Events 01: If the Person ID is invalid an error

message is displayed. The nurse then can decide either to search the

system with person identification information or redirect the person to a

Registrar.

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Bibliography and Suggested Reading

³Object-Oriented Software Engineering: A use Case Driven Approach´, by Ivar

Jacobsen

³Use Case Modeling: Capturing User Requirements´ by Edward Kenworthy

(http://www.zoo.co.uk/~z0001039/PracGuides/pg _ use _ cases.htm)

³Structuring Use Cases With Goals´ by Alistair Cockburn

(http://members.aol.com/acockburn/papers/usecases.htm)

³Use Cases Fundamentals´ by Alistair Cockburn

(http://members.aol.com/acockburn/papers/ AltIntro.htm)

³OOSC2: The Use Case Principle´ by Bertrand Meyer

(http://www.elj.com/elj/v1/n2/bm/use-cases/ )

³The Roles of Use Cases in Analysis´ by Daniel A. Rawsthorne, PhD

(http://www.pols.co.uk/usecasezone/UseCaseConcepts.html ) ³The Misuse of Use Cases´ By Dr. Timothy Korson

(http://www.software-architects.com/publications/korson/Korson9803om.htm )

³Constructing Useful Use Cases´ By Dr. Timothy Korson

(http://www.korson-mcgregor.com/publications/korson/usecase3/index.html )

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What are the use case modeling good, bad, and ugly?

Def ine: Actor , r ole, and use case

What are the diff erences between use cases andscenarios?

What are the diff erences between use case and a pr ocess?

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Discussion Questions

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Discuss the ways to analyze a

pr oblem.

What is a pr oblem?

What are the elements of pr oblem

analysis?

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Questions for the Next Lecture

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Task 1: Assignment # 1 is due on

___________. Late assignments are not acceptable.

Task 2: Check the web site for new postings

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Tasks for Next Lecture

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