Structure for dependability - computer-based systems from an interdisciplinary perspective

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers , or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. The use of registered names, trademarks, etc., in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Preface Computer-based systems are now essential to everyday life. They involve both technical (hardware/software) components and human beings as active participants. Whenever we fly aboard an aircraft or withdraw money from a cash point, a combination of humans, machines and software is supporting the delivery of the service. These systems and many others benefit from the miniaturisation and cost reduction of the hardware which has made it possible for computers to be embedded everywhere. An equally remarkable development is the software involved: today, systems are built which were literally unthinkable twenty or thirty years ago. Measured in terms of their function, the productivity of their creation has also advanced enormously (largely because of the software infrastructure). Even the dependability of the best of todays software is praiseworthy when one considers the complexity of the functionality provided. Solid engineering and the increasing adoption of methods based on firmly established theory are to be thanked here. However, in large and complex systems, there remain major challenges to achieving dependability when complex interactions exist between technical and human components. Large and complex things are understood as assemblages of simpler components: the way these components fit together is the structure of the system. Structure can be real and physical, or a subjective mental tool for analysis. It is often possible to view a complex system as having different structures: one useful view of the eventual structure will often be strongly related to the way …