Discovering Requirements

Ian Alexander consults and trains on requirements. He has co-authored 3 books including Writing Better Requirements (2002, Wiley), HTML 4 (1997, Addison-Wesley) and Scenarios, Stories, Use Cases (2004, Wiley), and has published many technical papers and popular articles, including regular contributions to the IEEE Software. He runs various requirements training courses for IET, JBA, DERA, QSS and UNICOM amongst others. Ljerka Beus-Dukic is a lecturer in software engineering and has taught Requirements Engineering for a number of years. Prior to joining academia, she worked in industry as a software engineer developing software for real-time applications. Ljerka is the author of many technical papers and was a contributor for the book (Powell D. (Ed.), A Generic Fault-Tolerant Architecture for Real-Time Dependable Systems, Kluwer Academic Publishers, 2001). She is on the programme committee for a number of conferences including ICCBSS and Euromicro and also worked on the EU funded GUARDS project. She has co-authored around 30 publications.

• Acknowledgements xvForeword xviiPart I: Discovering Requirement Elements 11 Introduction 31.1 Summary 41.2 Why You Should Read This Book 41.3 Simple but Not Easy 61.4 Discovered, Not Found 71.4.1 Many Different Situations 91.5 A Softer Process, at First 121.6 More than a List of ‘The System Shalls’ 161.6.1 A Network of Requirement Elements 161.6.2 Discovery as Search 181.7 A Minimum of Process: The Discovery Cycle 181.8 The Structure of this Book 201.8.1 Part I: Discovering Requirement Elements 211.8.2 Part II: Contexts for Discovery 221.9 Further Reading 221.9.1 Books on ‘Softer’ Approaches 221.9.2 Books on the Philosophical Background 231.9.3 Books on ‘Harder’ Approaches 242 Stakeholders 272.1 Summary 282.2 Discovering Stakeholders 282.2.1 Operational Stakeholders within ‘The System’ 302.2.2 Stakeholders in the Containing System and Wider Environment 302.3 Identifying Stakeholders 372.3.1 From your Sponsor or Client 372.3.2 With a Template such as the Onion Model 372.3.3 By Comparison with Similar Projects 402.3.4 By Analysing Context 402.4 Managing Your Stakeholders 412.4.1 Engaging with Stakeholders 412.4.2 Keeping Track of Stakeholders 422.4.3 Analysing Influences 422.4.4 Prioritising Stakeholders 432.4.5 Involving Stakeholders 452.4.6 The Integrated Project Team 452.5 Validating Your List of Stakeholders 452.5.1 Things To Check the Stakeholder Analysis Against 462.6 The Bare Minimum of Stakeholder Analysis 462.7 Next Steps: Requirements from Stakeholders 462.8 Exercise 492.9 Further Reading 493 Goals 513.1 Summary 523.2 Discovering Goals 523.2.1 Worked Example: Goals for a Spacecraft 543.2.2 Worked Example: Goals for a Restaurant 573.2.3 Worked Example: Tram Goals and Trade-offs 593.2.4 Finding Solutions to Goal Conflicts 623.2.5 Contexts for Discovering Goals 633.2.6 The Negative Side 653.3 Documenting Goals 683.3.1 Drawing Goal Diagrams 693.3.2 Other Ways of Documenting Goals 693.4 Validating Goals 713.4.1 Things To Check Goals Against 733.5 The Bare Minimum of Goals 733.6 Next Steps 733.7 Exercises 733.8 Further Reading 743.8.1 Goals 743.8.2 The Negative Side 743.8.3 The i∗ Goal Modelling Notation 744 Context, Interfaces, Scope 754.1 Summary 764.2 Introduction 764.3 A ‘Soft Systems’ Approach for Ill-Defined Boundaries 774.3.1 You are Part of the Soft System you are Observing 784.3.2 From Stakeholders to Boundaries 794.3.3 Identifying Interfaces 834.3.4 Documenting Interfaces 844.3.5 Validating your Choice of Boundary 864.4 Switching to a ‘Hard Systems’ Approach for Known Events 874.4.1 The Traditional Context Diagram 874.4.2 Scope as a List of Events 874.4.3 Expressing Event-handling Functions 894.4.4 Strengths and Weaknesses of Context Diagrams 924.4.5 Validating Interfaces and Events 934.4.6 Things To Check Context and Interfaces Against 954.5 The Bare Minimum of Context 954.6 Next Steps 954.7 Exercise 954.8 Further Reading 964.8.1 Soft Approaches 964.8.2 Event-Driven Approaches 964.8.3 Writing Requirements 965 Scenarios 975.1 Summary 985.2 Discovering Scenarios 985.2.1 Interviews, storytelling 995.2.2 Scenario Workshops 1015.2.3 Discovering Negative Scenarios 1075.3 Documenting Scenarios 1145.3.1 Index Cards, User Stories 1155.3.2 Storyboards 1165.3.3 Operational Scenarios 1185.3.4 Use Cases 1195.4 Summary 1245.5 Validating Scenarios 1245.5.1 Scenario Walkthroughs 1245.5.2 Animation, Simulation, Prototyping 1265.5.3 Things To Check Scenarios Against 1275.6 The Bare Minimum of Scenarios 1275.7 Next Steps 1275.8 Exercises 1285.9 Further Reading 1285.9.1 Storytelling 1285.9.2 Alternative Scenario Approaches 1285.9.3 Running Scenario Workshops 1295.9.4 The Principle of Commensurate Care 1296 Qualities and Constraints 1316.1 Summary 1326.2 What are Qualities and Constraints? 1326.2.1 A Rich Mixture 1326.2.2 Qualities that Govern Choices 1326.2.3 Constraints that Matter to People 1336.3 Discovering Qualities and Constraints 1336.3.1 Using Goals to Discover Qualities and Constraints 1346.3.2 Stakeholder Analysis to Discover Qualities and Constraints 1366.3.3 Using a Checklist to Discover Qualities and Constraints 1366.4 Documenting Qualities and Constraints 1416.4.1 Constraints 1426.4.2 Development (Process) Qualities 1466.4.3 Usage (Product) Qualities 1476.5 Validating Qualities and Constraints 1576.5.1 Things To Check Qualities and Constraints Against 1586.6 The Bare Minimum of Qualities and Constraints 1596.7 Next Steps 1596.8 Exercises 1596.9 Further Reading 1607 Rationale and Assumptions 1617.1 Summary 1627.2 The Value of Rationale 1627.3 Discovering Rationale and Assumptions 1637.3.1 Asking Why 1647.3.2 Looking for the word ‘will’ in vision statements, plans, etc 1657.3.3 Rationalising a Set of Requirements 1667.3.4 Inverting Risks 1687.4 Documenting Rationale 1697.4.1 Justification Text Field 1717.4.2 Lists of Assumptions, Risks, Issues and Decisions 1727.4.3 Traceability to Goals, Assumptions, etc 1737.4.4 Rationale Models 1787.4.5 The Goal Structuring Notation (GSN) 1827.5 Validating Rationale and Assumptions 1837.5.1 Rationale Walkthrough 1847.5.2 Analysis of Traceability 1847.5.3 Things To Check Rationale and Assumptions Against 1867.6 The Bare Minimum of Rationale and Assumptions 1877.7 Next Steps 1877.8 Exercise 1877.9 Further Reading 1877.9.1 Discovering Assumptions 1877.9.2 Reasoning 1887.9.3 Modelling Rationale 1887.9.4 Tracing to Goals 1887.9.5 Goal Structuring Notation (GSN) 1887.9.6 Satisfaction Arguments 1888 Definitions 1898.1 Summary 1908.2 Discovering Definitions 1908.2.1 Synonyms 1918.2.2 Homonyms 1938.3 Constructing the Project Dictionary 1948.3.1 Acronyms 1958.3.2 Definitions and Designations 1958.3.3 Roles (Operational Stakeholders) 1998.3.4 Data Definitions 2018.3.5 Constraints as Data 2028.4 Validating the Project Dictionary 2048.4.1 Validating Data Models 2058.4.2 Things To Check Definitions Against 2068.5 The Bare Minimum of Definitions 2068.6 Next Steps 2068.7 Exercise 2068.8 Further Reading 2068.8.1 Definitions and Designations 2068.8.2 Data Modelling 2079 Measurements 2099.1 Summary 2109.2 Discovering and Documenting Acceptance Criteria 2119.2.1 Acceptance Criteria for Behavioural Requirements 2129.2.2 Acceptance Criteria for Qualities 2169.2.3 Acceptance Criteria for Constraints 2189.2.4 Verification Method 2199.3 Validating Acceptance Criteria 2229.3.1 Testing from Day One 2229.4 Measuring Quality of Service (QoS) 2239.4.1 Example Service: Office Carpeting 2249.4.2 Two Opposite Approaches 2259.4.3 A Spectrum of Service Approaches 2269.4.4 Worked Example: QoS Measures for Food Preparation Services 2289.5 Validating QoS Measures 2309.5.1 Qualities of a Good QoS Measure 2309.5.2 Will your QoS Measures Work? 2319.5.3 Common QoS Measures 2329.5.4 Validating QoS with Negative Scenarios 2329.5.5 Things To Check Measurements Against 2339.6 The Bare Minimum of Measurement 2339.7 Next Steps 2339.8 Exercise 2339.9 Further Reading 23310 Priorities 23510.1 Summary 23610.2 Two Kinds of Priority 23610.3 Input Priority 23710.3.1 Discovering Input Priority 23710.3.2 Documenting Input Priority 24110.3.3 Validating Input Priority 24210.4 Output Priority 24310.4.1 Discovering Output Priority 24310.4.2 Documenting Output Priority 25110.4.3 Validating Output Priority 25310.5 Things To Check Priority Against 25410.6 The Bare Minimum of Priorities 25510.7 Next Steps 25510.8 Exercise 25510.9 Further Reading 25510.9.1 Triage 25510.9.2 Input Priority 25610.9.3 Boston Matrix 25610.9.4 Review Process 25610.9.5 Life Cycles 256Part II: Discovery Contexts 25711 Requirements from Individuals 25911.1 Summary 26011.2 Introduction 26011.3 Interviews 26111.3.1 Planning an Interview Campaign 26111.3.2 Planning Each Interview 26711.3.3 Documenting Interviews 26811.3.4 Validating Interview Findings 27311.4 Observation and ‘Apprenticeship’ 27411.4.1 Making Observations 27411.4.2 Being ‘Talked Through’ Operations 27611.4.3 Documenting Observations 27711.4.4 Validating Observations 28011.5 The Bare Minimum from Individuals 28011.6 Exercises 28011.7 Further Reading 28111.7.1 Interviewing 28111.7.2 Using Video 28111.7.3 Observation 28211.7.4 Tacit Knowledge 28211.7.5 Standard Types of Systems Analysis 28211.7.6 Informal Modelling Techniques 28211.7.7 Philosophy 28212 Requirements from Groups 28312.1 Summary 28412.2 The Goal of Group Work 28412.2.1 Unique Capabilities 28412.2.2 Obstacles 28512.2.3 Mediating Group Work (on one site or many) 28512.3 Workshops 28612.3.1 Define Workshop Mission 28612.3.2 Workshop Planning 28712.3.3 Workshop Rehearsal 28912.3.4 Workshop Setup 29012.3.5 Workshop Recording 29912.3.6 Validating Workshop Findings 30212.4 Group Media 30512.4.1 Project Wall 30512.4.2 Project Website 30612.4.3 Project Wiki 30712.4.4 Modelling Tool 30812.4.5 Requirements Management Tool 30912.4.6 Groupware and Working at a Distance 31012.4.7 The Role of Group Media 31212.5 The Bare Minimum from Groups 31412.6 Next Steps 31412.7 Exercise 31412.8 Further Reading 31512.8.1 Workshops 31512.8.2 Working in Groups 31513 Requirements from Things 31713.1 Summary 31813.2 Requirements Prototyping 31813.2.1 Purpose 31913.2.2 Techniques 31913.3 Reverse Engineering 33013.3.1 From an Existing Product 33013.4 Requirements Reuse 33713.4.1 Type 1: Naïve Reuse 33713.4.2 Type 2: Standardisation 33813.4.3 Type 3: Product Lines 33813.4.4 Tool Support for Reuse 33813.5 Validating Requirements from Things 34013.6 The Bare Minimum from Things 34013.7 Exercises 34013.8 Further Reading 34013.8.1 Prototyping 34014 Trade-offs 34314.1 Summary 34414.2 Optioneering: The Engineering of Trade-offs 34414.2.1 The Requirements-First Life-Cycle Myth 34414.2.2 An Optioneering Life Cycle 34514.2.3 The Optioneering Process 35014.2.4 Selecting the Winning Option 35214.2.5 Optioneering with PCA: A Worked Example 36014.3 Validating your Trade-offs 36714.4 The Bare Minimum of Trade-offs 36714.5 Next Steps 36714.6 Exercises 36814.7 Further Reading 36914.7.1 Trade-offs 36914.7.2 Statistics 37014.7.3 PCA 37014.7.4 Weighting Approaches 37014.7.5 Analytic Hierarchy Process (AHP) 37014.7.6 Quality Function Deployment (QFD) 37014.7.7 Questions, Options, Criteria (QOC) 37115 Putting it all Together 37315.1 Summary 37415.2 After Discovery 37415.2.1 Everything Depends on the Requirements 37415.2.2 Principles for the Requirements Chef 37515.3 The Right Process for your Project 37615.3.1 Case Study: A Retail IT Project 37715.3.2 Case Study: Transport Planning 37915.3.3 Requirements-Driven Project Management 38115.4 Organising the Requirements Specification 38515.4.1 Template 38515.4.2 Levels 38515.4.3 Can Use Cases Do Everything? 38615.4.4 Organising Product Functions 38615.4.5 Traditional ‘Shalls’ 38715.4.6 Relating Requirements of Different Types 38815.4.7 Conflicting Needs for Requirement Organisation 39015.4.8 The Benefit of Requirements (Traceability) Tools 39015.4.9 An Alternative View: Competing Approaches 39115.5 The Bare Minimum of Putting it all Together 39415.6 Further Reading 39415.6.1 Choosing and Tailoring Development Life Cycles 39415.6.2 Managing Projects From Requirements 39515.6.3 Classics for Inspiration and Reflection 39515.6.4 A Look Ahead 396Appendix A: Exercise Answers and Hints 397Appendix B: Getting the Level Right 405Appendix C: Tools for Requirements Discovery 411Appendix D: Template 423Bibliography 429Glossary 433Index 445