Writing Effective Use Cases

Use cases have never been this easy to understand -- or this easy to create! In Writing Effective Use Cases, Alistair Cockburn offers a hands-on, soup-to-nuts guide to use case development, based on the proven concepts he has refined through years of research, development, and seminar presentations. Cockburn begins by answering the most basic questions facing anyone interested in use cases: "What does a use case look like? When do I write one?" Next, he introduces each key element of use cases: actors, stakeholders, design scope, goal levels, scenarios, and more. Writing Effective Use Cases contains detailed guidelines, formats, and project standards for creating use cases -- as well as a detailed chapter on style, containing specific do's and don'ts. Cockburn shows how use cases fit together with requirements gathering, business processing reengineering, and other key issues facing software professionals. The book includes practice exercises with solutions, as well as a detailed appendix on how to use these techniques with UML. For all application developers, object technology practitioners, software system designers, architects, and analysts.

Alistair Cockburn is a recognized expert on use cases. He is consulting fellow at Humans and Technology, where he is responsible for helping clients succeed with object-oriented projects. He has more than twenty years of experience leading projects in hardware and software development in insurance, retail, and e-commerce companies and in large organizations such as the Central Bank of Norway and IBM.

0201702258AB07302002

Preface

xix

Acknowledgments

xxiii

Introduction

1

(20)

What Is a Use Case (More or Less)?

1

(6)

Buy Stocks over the Web

4

(1)

Get Paid for Car Accident

5

(1)

Register Arrival of a Box

6

(1)

Your Use Case Is Not My Use Case

7

(6)

Buy Something (Casual Version)

9

(1)

Buy Something (Fully Dressed Version)

9

(3)

``Discovering'' Requirements in New Territory

12

(1)

Steve Adolph

Requirements and Use Cases

13

(2)

Use Cases as Project-Linking Structure

14

(1)

The ``Hub-and-Spoke'' model of requirements

15

(1)

When Use Cases Add Value

15

(1)

Manage Your Energy

16

(1)

Warm Up with a Usage Narrative

17

(2)

Usage Narative: Getting ``Fast Cash''

18

(1)

Exercises

19

(2)

Part 1 The Use Case Body Parts

21

(117)

The Use Case as a Contract for Behavior

23

(12)

Interactions between Actors with Goals

23

(6)

Actors Have Goals

23

(1)

An actor with a goal calls on the responsibilities of another

24

(1)

Goals Can Fail

25

(1)

Interactions Are Compound

25

(2)

A Use Case Collects Scenarios

27

(1)

Striped trousers: Scenarios succeed or fail

28

(1)

The striped trousers showing subgoals

29

(1)

Contract between Stakeholders with Interests

29

(2)

The SuD serves the primary actor, protecting offstage stakeholders

30

(1)

The Graphical Model

31

(4)

Actors and stakeholders

32

(1)

Behavior

32

(1)

Use Case as responsibility invocation

33

(1)

Interactions as composite

33

(2)

Scope

35

(18)

A Sample In/Out List

36

(1)

Functional Scope

36

(2)

The Actor-Goal List

36

(1)

A Sample Actor-Goal List

37

(1)

The Use Case Briefs

37

(1)

Sample Use Case Briefs

38

(1)

Design Scope

38

(11)

Design scope can be any size

40

(1)

Using Graphical Icons to Highlight the Design Scope

40

(1)

Design Scope Examples

41

(1)

Enterprise-to-System Examples

41

(1)

Add New Service (Enterprise)

42

(1)

Add New Service (Acura)

42

(1)

Many Computers to One Application

43

(1)

Enter and Update Requests (Joint System)

43

(1)

Add New Service (into Acura)

44

(1)

Note New Service Request (in BSSO)

44

(1)

Update Service Request (in BSSO)

44

(1)

Note Update Request (in Acura)

44

(1)

Use case diagrams for Acura-BSSO

45

(1)

A combined use case diagram for Acura-BSSO

45

(1)

Nuts and Bolts Use Cases

46

(1)

Serialize Access to a Resource

46

(1)

Apply a Lock Conversion Policy

47

(1)

Apply an Access Compatibility Policy

48

(1)

Apply an Access Selection Policy

48

(1)

Make Service Client Wait for Resource Access

49

(1)

The Outermost Use Cases

49

(2)

Using the Scope-Defining Work Products

51

(1)

Exercises

51

(2)

Stakeholders and Actors

53

(8)

Stakeholders

53

(1)

The Primary Actor

54

(5)

Why Primary Actors Are Unimportant (and Important)

55

(2)

Actors versus Roles

57

(1)

Characterizing the Primary Actors

58

A Sample Actor Profile Table

56

(3)

Supporting Actors

59

(1)

The System Under Discussion

59

(1)

Internal Actors and White-Box Use Cases

59

(1)

Exercises

60

(1)

Three Named Goal Levels

61

(20)

Use Case levels

62

(1)

User Goals (Blue, Sea-Level)

62

(2)

Two Levels of Blue

63

(1)

Summary Level (White, Cloud/Kite)

64

(2)

Operate an Insurance Policy+

65

(1)

The Outermost Use Case Revisited

65

(1)

Subfunctions (Indigo/Black, Underwater/Clam)

66

(1)

Summarizing Goal Levels

66

(1)

Using Graphical Icons to Highlight Goal Levels

67

(1)

Finding the Right Goal Level

68

(2)

Finding the User's Goal

68

(1)

Raising and Lowering Goal Levels

69

(1)

Ask ``why'' to shift levels

69

(1)

A Longer Writing Sample: ``Handle a Claim'' at Several Levels

70

(9)

Handle a Claim (Business)

71

(1)

Evaluate Work Comp Claim

72

(1)

Handle a Claim (Systems) +

73

(2)

Register a Loss

75

(4)

Find a Whatever (Problem Statement)

79

(1)

Exercises

79

(2)

Preconditions, Triggers, and Guarantees

81

(6)

Preconditions

81

(2)

Minimal Guarantees

83

(1)

Success Guarantee

84

(1)

Triggers

84

(1)

Exercises

85

(2)

Scenarios and Steps

87

(12)

The Main Success Scenario

87

(3)

The Common Surrounding Structure

87

(2)

The Scenario Body

89

(1)

Action Steps

90

(8)

Guidelines

90

(1)

Use Simple Grammar

90

(1)

Show Clearly ``Who Has the Ball''

90

(1)

Write from a Bird's Eye View

91

(1)

Show the Process Moving Forward

91

(1)

Show the Actor's Intent, Not the Movements

92

(1)

Include a ``Reasonable'' Set of Actions

93

(1)

A transaction has four parts

93

(2)

``Validate,'' Don't ``Check Whether''

95

(1)

Optionally Mention the Timing

95

(1)

Idiom: ``User Has System A Kick System B''

96

(1)

Idiom: ``Do Steps x-y until Condition''

96

(1)

To Number or Not to Number

97

(1)

Exercises

98

(1)

Extensions

99

(12)

Extension Basics

99

(1)

The Extension Conditions

100

(6)

Brainstorm All Conceivable Failures and Alternative Courses

101

(1)

Make the Condition Say What Was Detected

102

(2)

Rationalize the Extensions List

104

(1)

Rollup Failures

105

(1)

Extension Handling

106

(4)

Indent Condition Handling

108

(1)

Failures within Failures

109

(1)

Creating a New Use Case from an Extension

109

(1)

Exercises

110

(1)

Technology and Data Variations

111

(2)

Technology variations using specialization in UML

112

(1)

Linking Use Cases

113

(6)

Sub Use Cases

113

(1)

Extension Use Cases

114

(3)

UML diagram of extension use cases

115

(1)

When to Use Extension Use Cases

116

(1)

Exercises

117

(2)

Use Case Formats

119

(19)

Formats to Choose From

119

(9)

Fully Dressed

119

(1)

Fully Dressed Use Case Template

119

(1)

Casual

120

(1)

Actually Login (Casual Version)

120

(1)

One-Column Table

121

(1)

One-Column Table Format of a Use Case

121

(1)

Two-Column Table

122

(1)

Two-Column Table

122

(1)

RUP Style

123

(1)

Register for Courses

124

(2)

If-Statement Style

126

(1)

Occam Style

126

(1)

Diagram Style

127

(1)

The UML Use Case Diagram

128

(1)

Forces Affecting Use Case Writing Styles

128

(4)

Consistency

130

(1)

Complexity

130

(2)

Standards for Five Project Types

132

(5)

For Requirements Elicitation

133

(1)

Elicitation Template---Oble a New Biscum

133

(1)

For Business Process Modeling

134

(1)

Business Process Template---Symp a Carstromming

134

(1)

For Sizing the Requirements

135

(1)

Sizing Template---Burble the Tramling

135

(1)

For a Short, High-Pressure Project

136

(1)

High-Pressure Template: Kree a Ranfath

136

(1)

For Detailed Functional Requirements

137

(1)

Use Case Name---Nathorize a Permion

137

(1)

Conclusion

137

(1)

Exercise

138

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Writing Effective Use Cases

Summary

Author Biography

Table of Contents

Supplemental Materials