ABSTRACT
In a system of realistic size, a further level of complexity is due to the combination and interaction of many features. For example, a modern mobile phone may provide the
CONTENTS 2.1 Introduction 11 2.2 Understanding the Requirement 13 2.3 Road Layout and Trac in the Real World 14 2.4 Simulation of Real-World Trac by Programming Objects 16 2.5 Initiative and Causality 17 2.6 Causality and Determination 19 2.7 Description Span 20 2.8 Forming Simulations 23 2.9 So ware System Design 24 2.10 Some General Observations 26 Acknowledgments 29 Disclaimer 29 References 29
functions of a telephone, a camera, a web browser, an e-mail client, a global positioning system (GPS) navigation aid, and several more. ese features can interact in many ways-a photograph taken by the camera can be transmitted in a telephone call-and the resulting complexity demands its own clearly understood structuring if the features interactions are to be useful and reliable. e functional structures created and understood by the designer must be intelligibly related to the parallel structures perceived by the users of the system. It is failure in this user-interface structuring that explains the diculty experienced by many users of digital television recorders, and the multitude of puzzled customers asking on Internet forums how to set the clock on their digitally controlled ovens.
