CS 325: Software Engineering February 3, 2015 Deriving Use Cases from Requirements Actors and Use...
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CS 325: Software Engineering February 3, 2015 Deriving Use Cases from Requirements • Actors and Use Cases • Creating A Use Case Diagram • Complex Use Case Diagrams
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Transcript of CS 325: Software Engineering February 3, 2015 Deriving Use Cases from Requirements Actors and Use...
CS 325: Software Engineering
February 3, 2015
Deriving Use Cases from Requirements• Actors and Use Cases• Creating A Use Case Diagram• Complex Use Case Diagrams
Actors and Use Cases
CS 325February 3, 2015Page 2
In a software system model, an actor is a role played by one of the system’s stakeholders who interacts with the system.
A use case is a business process that begins and ends with the actor and that accomplishes a business task for that actor.For example, for a software system that tests the effectiveness of a spam filter, one actor might be a system administrator who is responsible for ensuring that spam messages are blocked from the mailboxes of employees.Among the use cases for this actor:
• Testing how effectively a filter blocks spam
• Testing how effectively a filter permits “ham”
• Determining proper spam probabilities for blocking messages
Actors and Use Cases
CS 325February 3, 2015Page 3
Other actors who might interact with the spam filter tester:
• The developer of a spam filter dictionary, who might need to determine the effectiveness of a dictionary in blocking spam messages and not blocking ham messages.
• A commercial e-mail developer, who might use the tester to determine whether the particular phrasing of a message would cause it to be blocked as spam.
Creating A Use Case Diagram
CS 325February 3, 2015Page 4
• Start with the system boundary and the actors.
SystemAdministrator
CommercialE-Mailer
Spam DictionaryDeveloper
SystemAdministrator
CommercialE-Mailer
Test WhetherPlanned Message Will Be
Interpreted As Spam
Test Whether Spam DictionaryWill Correctly Identify
Common Spam Messages
Test Whether Spam DictionaryWill Incorrectly Identify
Ham Messages As Spam
Determine AppropriateSpam Probabilities
Spam DictionaryDeveloper
• Insert the use cases and the associations.
• Note any extensions, inclusions, and generalizations.
SystemAdministrator
CommercialE-Mailer
Test WhetherPlanned Message Will Be
Interpreted As Spam
Test Whether Spam DictionaryWill Correctly Identify
Common Spam Messages
Test Whether Spam DictionaryWill Incorrectly Identify
Ham Messages As Spam
Determine AppropriateSpam Probabilities
<<include>>
<<include>> Spam DictionaryDeveloper
Creating A Use Case Diagram
CS 325February 3, 2015Page 5
Consider a student information system (SIS) with the following features:
• Student enrollment tools for online registration, class schedule checking, course cancellation notification, wait listing for full classes, submitting transfer credits
• Academic advising support tools for degree auditing, transfer credit equivalencies, prerequisite checking, course requirement overrides
• Faculty tools for generating class rosters, recording course grades, posting new assignments, retrieving laboratory grades
• Administrative tools for enrollment analysis, classroom scheduling, awarding financial aid, inclement weather notifications
Student
TransferStudent
AcademicAdvisor
Professor
InstructorAdministrator
Student
TransferStudent
AcademicAdvisor
Professor
Instructor
RegisterOnline
CheckSchedule
GetWaitlisted
DropCourse
SubmitTransferCredit
Administrator
Student
TransferStudent
AcademicAdvisor
Professor
Instructor
RegisterOnline
CheckSchedule
GetWaitlisted
DropCourse
SubmitTransferCredit
Administrator
AuditDegree
CheckPrereqs
EvaluateTransferCredit
Override Course
Requirements
Student
TransferStudent
AcademicAdvisor
Professor
Instructor
RegisterOnline
CheckSchedule
GetWaitlisted
DropCourse
SubmitTransferCredit
Administrator
AuditDegree
CheckPrereqs
EvaluateTransferCredit
Override Course
Requirements
GenerateRoster
RecordGrades
PostAssignment
RetrieveLab Grades
Creating A Use Case Diagram
CS 325February 3, 2015Page 6
Student
TransferStudent
AcademicAdvisor
Professor
Instructor
RegisterOnline
CheckSchedule
GetWaitlisted
DropCourse
SubmitTransferCredit
Administrator
AuditDegree
CheckPrereqs
EvaluateTransferCredit
Override Course
Requirements
GenerateRoster
RecordGrades
PostAssignment
RetrieveLab Grades
AnalyzeEnrollment
ScheduleClassroom
AwardFinancial Aid
Issue WeatherWarning
Complex Use Case Diagrams
CS 325February 3, 2015Page 7
Student
AcademicAdvisor
CourseInstructor
Add CourseBefore First
Week
Drop CourseBefore Eleventh
Week
DepartmentChair
CollegeDean
Add CourseDuring First
Week
Add CourseDuring Second
Week
Add CourseAfter Second
Week
Drop CourseBetween
Weeks 11-13
The whole point of a use case diagram is to clarify the development team’s understanding of the requirements of the planned system.An overly complicated diagram may obscure that understanding rather than clarifying it.
Complex Use Case Diagrams
CS 325February 3, 2015Page 8
Splitting the diagram into multiple diagrams, in this case representing smaller subsystems, improves their overall clarity.Also note how the use of the inclusion relationship eliminates potentially confusing redundancies.
Student
AcademicAdvisor
CourseInstructor
Add CourseBefore First
Week
DepartmentChair
CollegeDean
Add CourseDuring First
Week
Add CourseDuring Second
Week
Add CourseAfter Second
Week
<<include>>
<<include>>
<<include>>
Student
AcademicAdvisor
CourseInstructor
Drop CourseBefore Eleventh
Week
Drop CourseBetween
Weeks 11-13
