Fall 2002 SJSU -- CmpE
Object-Oriented Analysis & Design
Dr. M.E. Fayad, ProfessorComputer 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
Fall 2002 SJSU – CmpE M.E. Fayad L09-S2 Use Case Modeling
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Lesson 12:Use Case Modeling
Fall 2002 SJSU – CmpE M.E. Fayad L09-S3 Use Case Modeling
Lesson Objectives
Objectives
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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 & University Registration
Fall 2002 SJSU – CmpE M.E. Fayad L09-S4 Use Case Modeling
What is use case modeling?
use case model: a view of a system that emphasizes the behavior as it appears to outside users. A use case model partitions system functionality into transactions (‘use cases’) that are meaningful to users (‘actors’).
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S5 Use Case Modeling
Use Case Modeling: Core Elements
Construct Description Syntax
use case A sequence of actions, including variants, 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 interacting with these use cases.
system boundary
Represents the boundary between the physical system and the actors who interact with the physical system.
UseCaseNam e
ActorNam e
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S6 Use Case Modeling
Construct 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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Fall 2002 SJSU – CmpE M.E. Fayad L09-S7 Use Case Modeling
Construct 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 behaviordefined for the base use case.
Use Case Modeling: Core Relationships (cont’d)
<<include>>
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S8 Use Case Modeling
Shows use cases, actor and their relationships
Use case internals can be specified by text and/or interaction diagrams
Kinds– use case diagram– use case description
Use Case Diagram Tour
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S9 Use Case ModelingFig. 3-44, UML Notation Guide
Customer
Supervisor
SalespersonPlace
Establishcredit
Check
Telephone Catalog
F ill orde rs
Shipping Clerk
status
order
Use Case Model
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S10 Use Case ModelingFig. 3-45, UML Notation Guide
Use Case Diagram: Relationships
additional requests :
OrderProduct
SupplyArrange
«include»«include»«include»
RequestCatalog
«extend»Extension points
PaymentCustomer Data
after creation of the order
Place Order
1 * the salesperson asks forthe catalog
Fall 2002 SJSU – CmpE M.E. Fayad L09-S11 Use Case ModelingFig. 3-46, UML Notation Guide
Use Case Diagram: Actor Relationships
EstablishCredit
PlaceOrder
Salesperson
Supervisor
1 *
1 *
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S12 Use Case Modeling
Use Case Description: Change Flight Actors: traveler, client account db, airline reservation system Preconditions:
Traveler has logged on to the system and selected ‘change flight itinerary’ option
Basic course System retrieves traveler’s account and flight itinerary from client account database System asks traveler to select itinerary segment she wants to change; traveler selects itinerary segment. System asks traveler for new departure and destination information; traveler provides information. If flights are available then … System displays transaction summary.
Alternative courses If no flights are available then …
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S13 Use Case Modeling
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 structural and behavioral models from it.
If you are not using a use-case driven method– make sure that your use cases are consistent
with your structural and behavioral models.
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S14 Use Case Modeling
Use Case Modeling Tips
Make sure that each use case describes a significant chunk of system usage that is understandable by both domain experts and programmers
When defining 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 actors who are required Large numbers of use cases should be organized into packages
Fall 2002 SJSU – CmpE M.E. Fayad L09-S15 Use Case Modeling
Sample Problem Statement: Library System
You have been contracted to develop a computer system for a university library. The library currently uses a 1960s program, written in an obsolete language, for some simple bookkeeping tasks, and a card index, for user browsing. You are asked to build an interactive system which handles both of these aspects online.*
*Example from: “Using UML”, by: Pooley and Stevens
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S16 Use Case Modeling
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 the
users have to do– Users can be, and frequently are, hostile.
Why? What can be done about it? 16
Fall 2002 SJSU – CmpE M.E. Fayad L09-S17 Use Case Modeling
The Use Case Model
We must now identify the users of the system and the tasks they must undertake with the system. The details of the use case should be documented, using a Use Case Template.
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S18 Use Case Modeling
The Use Case Template
Use Case TemplatePACKAGE: _________________ [Description (an over view of the package)].USE CASES: [A package will have one or more Use Cases].Use Case No.: [1.1]Use Case Title: [A descriptive title]
[Ex. adding a new patient, or adding a new role].Actors: _______, _______, _______, _______.
[Any users of the Use Case, ex. human, machine, other systems or subsystems].Corresponding Roles: _______, _______, _______, _______.
[There is a different role per actor in every Use Case].Classes: _______, _______, _______, _______.
[List all the classes within the Use Case Description].Enduring Business Themes (EBT): _______, _______, _______Business Objects (BO): _______, _______, _______, _______.Industrial Objects (IO): _______, _______, _______, _______.
[This 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 Use Case]. 18
Fall 2002 SJSU – CmpE M.E. Fayad L09-S19 Use Case ModelingCopyright © 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 when the use case is executed
Typical contents– How the use case starts and ends– Normal flow of events– Alternate flow of events– Exceptional flow of events
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S20 Use Case Modeling
Actors
An actor is someone or something that must interact with the system under development
BookBorrower
Browser
Librarian
JournalBorrower
Fall 2002 SJSU – CmpE M.E. Fayad L09-S21 Use Case Modeling
Use CasesActors 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
Fall 2002 SJSU – CmpE M.E. Fayad L09-S22 Use Case Modeling
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: – Borrow 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: “Using UML”, by: Pooley and Stevens 22
Fall 2002 SJSU – CmpE M.E. Fayad L09-S23 Use Case Modeling
Use Case Diagram for the first iteration
*Example from: “Using UML”, by: Pooley and Stevens
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S24 Use Case Modeling
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 books may 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 sometimes disposed of. The current year’s journals are sent away to be bound into volumes at the end of each year.*
*Example from: “Using UML”, by: Pooley and Stevens
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S25 Use Case Modeling
What Requirements would an ideal system satisfy?
Borrowing: 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. There may in future be a requirement for users to be able to extend the loan of a book if it is not reserved.
Browsing: 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.*
*Example from: “Using UML”, by: Pooley and Stevens
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S26 Use Case Modeling
Use Cases for the library
*Example from: “Using UML”, by: Pooley and Stevens
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Fall 2002 SJSU – CmpE M.E. Fayad L09-S27 Use Case Modeling
Example II: University Registration
The ESU University wants to computerize their registration system– The Registrar sets up the curriculum for a semester
• One course may have multiple course offerings– Students select 4 primary courses and 2 alternate courses– Once a student registers for a semester, the billing system is
notified so the student may be billed for the semester– Students may use the system to add/drop courses for a period of
time after registration– Professors use the system to receive their course offering rosters– Users of the registration system are assigned passwords which
are used at logon validation
Fall 2002 SJSU – CmpE M.E. Fayad L09-S28 Use Case ModelingCopyright © 1997 by Rational Software Corporation
Actors
Student
Registrar
Professor
Billing System 28
Fall 2002 SJSU – CmpE M.E. Fayad L09-S29 Use Case ModelingCopyright © 1997 by Rational Software Corporation
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
Fall 2002 SJSU – CmpE M.E. Fayad L09-S30 Use Case ModelingCopyright © 1997 by Rational Software Corporation
Maintain Curriculum: Flow of Events (description)
This use case begins when the Registrar logs onto the Registration System and enters his/her password. The system verifies that the password is valid (E-1) and prompts the Registrar to select the current semester or a future semester (E-2). The Registrar enters the desired semester. The system prompts the professor to select the desired activity: ADD, DELETE, REVIEW, or QUIT.
If the activity selected is ADD, the S-1: Add a Course subflow is performed.
If the activity selected is DELETE, the S-2: Delete a Course subflow is performed.
If the activity selected is REVIEW, the S-3: Review Curriculum subflow is performed.
If the activity selected is QUIT, the use case ends. 30
Fall 2002 SJSU – CmpE M.E. Fayad L09-S31 Use Case ModelingCopyright © 1997 by Rational Software Corporation
Use Case Model Use case diagrams are created to visualize the relationships
between actors and use cases
Student
Registrar
Professor
Maintain Schedule
Maintain Curriculum
Request Course Roster
Billing System
Fall 2002 SJSU – CmpE M.E. Fayad L09-S32 Use Case ModelingCopyright © 1997 by Rational Software Corporation
Uses and Extends Use Case Relationships
As the use cases are documented, other use case relationships may be discovered
– A uses relationship shows behavior that is common to one or more use cases
– An extends relationship shows optional behavior
Register for courses
<<uses>>
Logon validation<<uses>>
Maintain curriculum
Fall 2002 SJSU – CmpE M.E. Fayad L09-S33 Use Case Modeling
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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Fall 2002 SJSU – CmpE M.E. Fayad L09-S34 Use Case Modeling
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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Fall 2002 SJSU – CmpE M.E. Fayad L09-S35 Use Case Modeling
Acknowledgements
Object Modeling with OMG UML: Introduction to UML
– Cris Kobryn– Chief Scientist, InLine Software
Co-Chair UML Revision Task ForceAugust 2000
“Using UML: Software Engineering With Objects and
Components” by: Rob Pooley and Perdita Stevens
“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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Fall 2002 SJSU – CmpE M.E. Fayad L09-S36 Use Case Modeling
Use Case No.: 1.1.1 Use Case Title: Find Candidate Actors: 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)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S37 Use Case Modeling
Description of the Use Case: 1. The Registrar enters the information about a person into the
System. 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 its
CandidateListGenerator and its set of PersonProfiles and returns it to the System.
6. The Registrar chooses the candidate from the list that represents the person.
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Sample Use Case from Philips Project (2)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S38 Use Case Modeling
Use Case No.: 1.2.1 Use Case Title: Register New ID Actors: 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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Sample Use Case from Philips Project (3)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S39 Use Case Modeling
Description of the Use Case: 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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Sample Use Case from Philips Project (4)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S40 Use Case Modeling
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 in the system with a new ID or pick one from the selection list.
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Sample Use Case from Philips Project (5)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S41 Use Case Modeling
Use Case No.: 1.3.1
Use Case Title: Get Patient Profile using Patient ID
Actors / 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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Sample Use Case from Philips Project (6)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S42 Use Case Modeling
Description of the Use Case:
1. The Nurse enters the Person ID for the person.
2. The Person Identification system determines the validity of the Person 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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Sample Use Case from Philips Project (7)
Fall 2002 SJSU – CmpE M.E. Fayad L09-S43 Use Case Modeling
Bibliography and Suggested Reading “Object-Oriented Software Engineering: A use Case Driven Approach”, by Ivar
Jacobsen “Use Case Modeling: Capturing User Requirements” by Edward Kenworthy (
http://www.zoo.co.uk/~z0001039/PracGuides/pg_use_cases.htm) “Structuring Use Cases With Goals” by Alistair Cockburn
(http://members.aol.com/acockburn/papers/usecases.htm) “Use Cases Fundamentals” by Alistair Cockburn
(http://members.aol.com/acockburn/papers/AltIntro.htm) “OOSC2: The Use Case Principle” by Bertrand Meyer (
http://www.elj.com/elj/v1/n2/bm/use-cases/ ) “The Roles of Use Cases in Analysis” by Daniel A. Rawsthorne, PhD
(http://www.pols.co.uk/usecasezone/UseCaseConcepts.html ) “The Misuse of Use Cases” By Dr. Timothy Korson
(http://www.software-architects.com/publications/korson/Korson9803om.htm ) “Constructing Useful Use Cases” By Dr. Timothy Korson
(http://www.korson-mcgregor.com/publications/korson/usecase3/index.html )
Fall 2002 SJSU – CmpE M.E. Fayad L09-S44 Use Case Modeling
• What are the use case modeling good, bad, and ugly?
• Define: Actor, role, and use case
• What are the differences between use cases and scenarios?
• What are the differences between use case and a process?
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Discussion Questions
Fall 2002 SJSU – CmpE M.E. Fayad L09-S45 Use Case Modeling
Discuss the ways to analyze a problem.
What is a problem?
What are the elements of problem analysis?
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Questions for the Next Lecture
Fall 2002 SJSU – CmpE M.E. Fayad L09-S46 Use Case Modeling
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