Experience has shown us that investment in the requirements process saves time, money, and effort. Yet, development efforts consistently charge ahead without investing sufficiently in the requirements process. We are so intent to develop the technical solutions that we are unwilling to take the time and effort to understand and meet the real customer needs.
--From the Foreword by Ralph R. Young, author of Effective Requirements Practices
If you are involved in the systems engineering process, in any company -- from transport and telecommunications, to aerospace and software -- you will learn how to write down requirements to guarantee you get the systems YOU need.What skills will I learn?
1. Introduction 9
1. Introduction 9
1.1 Why do requirements matter? 9
1.2 Who are requirements for? 12
1.3 Different names for requirements 13
1.4 Different types of specification 14
1.5 The challenge of writing better requirements 15
1.6 The requirements writing process 18
2. Identifying the stakeholders 21
2.1 Different types of stakeholder 21
2.2 Your house extension: a simple case? 22
2.3 A practical approach to identifying stakeholders 23
Exercise 1: Listing the stakeholders 23
3. Gathering requirements from stakeholders 26
3.1 Possible techniques 26
Exercise 2: Asking 'why?' 28
3.2 Interviews 28
3.3 Workshops 32
3.4 Experiencing life as a user 36
3.5 Observing users at work 36
3.6 Acting out what needs to happen 36
3.7 Prototypes 38
4. Other sources of requirements 40
4.1 Possible sources 40
Exercise 3: Extracting requirements from source documents 44
Exercise 4: Extracting requirements from a memo 45
4.2 Getting requirements for mass-market products 45
4.3 User requirements in subsystem projects 46
5. Structuring the requirements 47
5.1 You need structure as well as text 47
5.2 Breaking the problem down into steps 48
5.3 Organizing requirements into scenarios 50
5.4 Examples of goal decomposition 52
Exercise 5: A structure for user requirements 53
5.5 Handling exceptions 53
Exercise 6: Could anything go wrong here? 54
Exercise 7: Exceptions 55
5.6 Examples and exercises in requirement structure 57
Exercise 8: Creating a heading structure 57
Exercise 9: The right document for each subject 57
Exercise 10: Wrongly placed requirements 58
6. Requirements in context 59
6.1 The user requirements document 59
6.2 Organizing the constraints 60
Exercise 11: Writing constraints 64
6.3 Defining the scope 64
Exercise 12: Restricting the scope 65
6.4 Requirement attributes 65
6.5 Keeping track of the requirements 67
7. Requirements writing 70
7.1 Quality, not perfection 70
7.2 Sketch, then improve 70
7.3 Anatomy of a good requirement 70
7.4 Guidelines for good requirements 71
7.5 Don't write like this 72
Exercise 13: Good requirements 75
Exercise 14: Writing requirements for familiar domestic systems 75
Exercise 15: Ambiguous requirements 76
8. Checking and reviewing 78
8.1 Checking the document structure with users 78
8.2 Checking the requirements 80
Exercise 16: Checking individual requirements 81
Exercise 17: Checking a set of requirements 82
8.3 Reviewing 83
8.4 Success - the reviewed document 85
Exercise 18: Reviewing 85
A: Answers to exercises 87
Exercise 1: Listing the stakeholders 87
Exercise 2: Asking 'why?' 87
Exercise 3: Extracting requirements from source documents 87
Exercise 4: Extracting requirements from a memo 88
Exercise 5: A structure for user requirements 88
Exercise 6: Could anything go wrong here? 89
Exercise 7: Exceptions 89
Exercise 8: Creating a heading structure 90
Exercise 9: The right document for each subject 90
Exercise 10: Wrongly placed requirements 90
Exercise 11: Writing constraints 91
Exercise 12: Restricting the scope 92
Exercise 13: Good requirements 92
Exercise 14: Writing requirements for familiar domestic systems 93
Exercise 15: Ambiguous requirements 93
Exercise 16: Checking individual re
It isn't that they can't see the solution. It is that they can't see the problem.
G. K. Chesterton
Requirements are the key to project success. We all know this, but we often forget n and pay the price. Many projects, both in industry and in the public sector, fail to do what is needed. They deliver late, over budget, and poor quality. Missing out on requirements is disastrous.
Writing Better Requirements is designed as a short, convenient overview for practising systems engineers and others who find they need to write requirements. Because it is about practical techniques, it should be useful in many different kinds of system and software project. We aim to enable readers to write requirements good enough for successful systems to be specified, designed, and tested against them.
This book should also form a useful introduction for students who want to learn how to get started with requirements.
This book specifically focuses on how to discover and express requirements. It is not about system specification, nor how to make a design that meets user needs, nor even about how users should ensure their requirements are met.Since users own the requirements, these must be expressed in a way users can understand. This book treats requirements as simple pieces of text, supported by operational scenarios and informal diagrams. Many attempts have been made to improve on these simple means, using more formal structures and notations with varying success. We have not tried to cover all these approaches.
To place requirements in context, the book must of course cover some aspects of the development process. Project management, verification, quality assurance, and the development life cycle are all closely linked with requirements n indeed each of these areas is meaningless in isolation. But in this book, we concentrate on the tasks of capturing and writing requirements. Each chapter contains exercises to help readers to practice their skills.
We recommend some good books for readers who want to go beyond writing good requirements to other aspects of systems and requirements engineering.
This book is meant to be read in the order in which it is written, taking the reader through a disciplined process of identifying, gathering, organizing, and reviewing. This is vital for success.
Each chapter introduces a stage in the requirements process. Key terms are defined informally, explained, and illustrated with examples and exercises to develop the practical skills of good requirements writing.
These skills involve looking at problems, dealing with people, looking critically at what is being written, and reviewing requirements effectively. Reviewing is to some extent a separate skill and can be looked at separately; the others belong together in a more or less strict sequence.
We begin by illustrating the importance of requirements. You may need this chapter to convince other people that they have a problem. Too many projects have poor requirements, and never recover. If you are already convinced, you can skip this introductory chapter.
We then show in a non-technical way how to define a problem, in close co-operation with the only people who know what the problem is, the users. The body of the book steps through the process, looking at:
All the chapters in the body of the book contain practical exercises for the reader. These are designed to take about half an hour each. Some are sufficiently open-ended for more extended self-instruction, or student projects. We recommend that readers attempt each exercise, at least briefly, to get an actual feeling for the difficulties involved. At the back of the book are short answers to all the questions, with hints to the reader for more complete projects.
If the message of this book can be stated in a sentence, it is:
Get agreement on what people want, before attempting to create solutions.
Finding out what is needed, instead of rushing into presumed solutions, is the key to every aspect of system development. Most technical problems can be solved, given determination, patience, a skilled team n and a good definition of the problem to be solved.
We would like to thank the anonymous reviewers who checked the book so carefully; our wives and families for tolerating us while we wrote; and all our consultancy, training and workshop clients who experienced the material first-hand and showed us the way it needed to be explained. We are specially grateful to Richard Marshall for reading an early draft, and to Professor Ken Jackson for his perceptive and precise comments.