Introduction

Abstract

Despite its huge importance for industry, the process of approving software-based equipment for executing safety critical functions remains highly complex, poorly understood and, as a result, often not efficiently mastered by regulators, licensees and suppliers; “Understanding Computer System Dependability” might have been a more appropriate title for this work.

The difficulties – some are devilishly complex – are both practical and theoretical. In practice, several engineering specialties need to be applied, in the field of computer hardware and software design and engineering, and also in the application domain in which the computer is embedded. To add to the difficulty, several industrial sectors still think that today complex software systems can be developed in the same ways analogue instrumentation and control systems were manufactured thirty five years ago, with more or less the same requirement specification approach, production tools an test strategies; a state of affairs which does not contribute to produce justifiably dependable software.