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Contents xv

6.3.2 What do we mean by "needs"? 172
6.3.3 How do you generate alternative designs? 174
6.3.4 How do you choose among alternative designs? 179
6.4 Lifecycle models: showing how the activities are related I 82
6.4.1 A simple lifecycle model for interaction design 186
6.4.2 Lifecycle models in software engineering 187
6.4.3 Lifecycle models in HCI 192
Interview with Gillian Crampton Smith 198

Chapter 7 Identifying needs and establishing requirements 201
7.1 Introduction 201
7.2 What, how, and why? 202
7.2.1 What are we trying to achieve in this design activity? 202
7.2.2 How can we achieve this? 202
7.2.3 Why bother? The importance of getting it right 203
7.2.4 Why establish requirements? 204
7.3 What are requirements? 204
7.3.1 Different kinds of requirements 205
7.4 Data gathering 21 0
7.4.1 Data-gathering techniques 21 1
7.4.2 Choosing between techniques 21 5
7.4.3 Some basic datmgathering guidelines 21 6
7.5 Data interpretation and analysis 21 9
7.6 Task description 222
7.6.1 Scenarios 223
7.6.2 Use cases 226
7.6.3 Essential use cases 229
7.7 Task analysis 231
7.7.1 Hierarchical Task Analysis (HTA) 231
Interview with Suzanne Robertson 236

Chapter 8 Design, prototyping and construction 239
1
8.1 lntroduction 239
8.2 Prototyping and construction 240
8.2.1 What is a prototype? 240
8.2.2 Why prototype? 241
8.2.3 Low-fidelity prototyping 243
8.2.4 High-fidelity prototyping 245
8.2.5 Compromises in prototyping 246