Scenarios, Stories, Use Cases: Through the Systems Development Life-Cycle

CHAPTER 1

INTRODUCTION: SCENARIOS IN SYSTEM DEVELOPMENT

Ian Alexander

Scenario Plus, London, UK

SCENARIOS ARE a powerful antidote to the complexity of systems and analysis. Telling stories about systems helps ensure that people—stakeholders—share a sufficiently wide view to avoid missing vital aspects of problems. Scenarios vary from brief stories to richly structured analyses, but are almost always based on the idea of a sequence of actions carried out by intelligent agents. People are very good at reasoning from even quite terse stories, for example detecting inconsistencies, omissions, and threats with little effort. These innate human capabilities give scenarios their power. Scenarios are applicable to systems of all types, and may be used at any stage of the development life cycle for different purposes.

CONTEXT

Scenarios are simple, human things. This book reveals that there are many possible variations on the theme, and the Scope section below introduces some of the concepts; but the basic idea is just a story: someone does this, someone else does that:

The driver walks towards the car and presses his key.

The car recognises the driver, unlocks the doors, and adjusts the driving seat, steering wheel, radio, and mirrors to the driver's preferred settings.

“Scenarios are arguably the starting point for all modelling and design” (Sutcliffe 2003). Since systems either do something that somebody wants, or are shelfware, and scenarios describe how to do things, it seems hard ...