1. Joey F. George, Dinesh Batra, Joseph S. Valacich, Jeffrey A. Hoffer
Chapter 6: Structuring Systems Requirements: Use Case Description and Diagrams
Object-Oriented Systems Analysis and Design
Joey F. George, Dinesh Batra,
Joseph S. Valacich, Jeffrey A. Hoffer
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2. Chapter Objectives After studying this chapter you should be able to:
Understand how to structure requirements with use case diagrams.
Explain the basics of use case construction using UML standards.
Construct use case diagrams.
Write text-based use cases.
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4. What Is Requirements Structuring?
The process of analyzing, organizing, and modeling the requirements obtained via interviews, questionnaires, observation, and document analysis
Relevant UML models include use cases, class diagrams, interaction diagrams, and activity or statechart diagrams
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5. Use Case Deliverables Use case diagrams
Written descriptions of use-case contents
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7. UML Use Case Diagram Symbols
Actor
Boundary
Connection
Include relationship
Extend relationship
<<include>>
<<extend>>
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8. What Is a Use Case?
A depiction of a system’s behavior or functionality under various conditions as the system responds to requests from users
Full functioning for a specific business purpose
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9. What Is an Actor? An external entity that interacts with the system
Most actors represent user roles, but actors can also be external systems.
An actor is a role, not a specific user; one user may play many roles, and an actor may represent many users.
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10. What Is a Boundary?
The dividing line between the system and its environment
- Use cases are within the boundary.
- Actors are outside of the boundary.
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11. What Is a Connection? An association between an actor and a use case
Depicts a usage relationship
Connection does not indicate data flow
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12. What Is an <<include>> Relationship?
A connection between two use cases
Indicates a use case that is used (invoked) by another use case
Links to general purpose functions, used by many other use cases
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14. What Is an <<extend>> Relationship?
A connection between two use cases
Extends a use case by adding new behavior or actions
Specialized use case extends the general use case
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15. What Is a Stereotype A construct that extends the UML vocabulary
Adds new meanings to existing entities
Depicted with << >> delimiters
<<extend>> and <<include>> are stereotypes
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16. Use Case Diagram in MS Visio
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18. Include vs. Extend
Use <<extend>> if you want to model an extension to, or a variation of, a complete use case that exists in its own right
Use <<include>> if you want to factor the common behavior among two or more use cases into a single generalized use case
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19. Actors can be grouped in generalization categories.
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20. Written Use Cases
Document containing detailed specifications for a use case
Contents can be written as simple text or in a specified format
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22. Level of Use Case
Refers to degree of detail in the use case description
Five suggested levels (Cockburn)
White – as seen from clouds
Kite – “birds-eye view”
Blue – sea-level view
Fish – below sea-level
Black – bottom of the sea
summary
detail
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23. summary
detail
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24. Sample Format for Written Use Case
Title – descriptive name, matches name in use case diagram
Primary actor – usually a user role
Stakeholders – any group or individual with an interest in the function of the use case
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25. Sample Format for Written Use Case (Continued)
Precondition – conditions that must be satisfied in order to execute the use case
Minimal guarantee – outputs that can be expected if the service attempt failed
Success guarantee – outputs that can be expected if the service succeeds
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26. Sample Format for Written Use Case (Continued)
Trigger – an event or action that initiates the use case
Main success scenario – description of sequence of interactions between actor and use case during the use case execution
Extensions – detailed description of how errors are dealt with
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27. A sample written use case at kite level
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28. Corresponds with Step 1 of kite-level use case
Use case at sea level
Corresponds with Step 1 of kite-level use case
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29. Corresponds with Step 2 of kite-level use case
Use case at sea level
Corresponds with Step 2 of kite-level use case
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30. Guidelines for Good Use Cases
Choose a good name
Illustrate a complete behavior
Identify a completable behavior
Provide “inverse” use cases
Limit each use case to one behavior
Represent the actor’s point of view
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