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Joey F. George, Dinesh Batra, Joseph S. Valacich, Jeffrey A. Hoffer

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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 © Prentice Hall, 2007

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. © Prentice Hall, 2007

3 © Prentice Hall, 2007

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 © Prentice Hall, 2007

5 Use Case Deliverables Use case diagrams
Written descriptions of use-case contents © Prentice Hall, 2007

6 © Prentice Hall, 2007

7 UML Use Case Diagram Symbols
Actor Boundary Connection Include relationship Extend relationship <<include>> <<extend>> © Prentice Hall, 2007

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 © Prentice Hall, 2007

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. © Prentice Hall, 2007

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. © Prentice Hall, 2007

11 What Is a Connection? An association between an actor and a use case
Depicts a usage relationship Connection does not indicate data flow © Prentice Hall, 2007

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 © Prentice Hall, 2007

13 © Prentice Hall, 2007

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 © Prentice Hall, 2007

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 © Prentice Hall, 2007

16 Use Case Diagram in MS Visio
© Prentice Hall, 2007

17 © Prentice Hall, 2007

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 © Prentice Hall, 2007

19 Actors can be grouped in generalization categories.
© Prentice Hall, 2007

20 Written Use Cases Document containing detailed specifications for a use case Contents can be written as simple text or in a specified format © Prentice Hall, 2007

21 © Prentice Hall, 2007

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 © Prentice Hall, 2007

23 summary detail © Prentice Hall, 2007

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 © Prentice Hall, 2007

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 © Prentice Hall, 2007

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 © Prentice Hall, 2007

27 A sample written use case at kite level
© Prentice Hall, 2007

28 Corresponds with Step 1 of kite-level use case
Use case at sea level Corresponds with Step 1 of kite-level use case © Prentice Hall, 2007

29 Corresponds with Step 2 of kite-level use case
Use case at sea level Corresponds with Step 2 of kite-level use case © Prentice Hall, 2007

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 © Prentice Hall, 2007


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