SOFTWARE RELIABILITY AND RECOVERY TECHNIQUES The general approach in this book is to treat reliability as a system problem and to decompose the system into a hierarchy of related subsystems or components. The reliability of the entire system is related to the reliability of the components by some sort of structure function in which the components may fail independently or in a dependent manner. The discussion that follows will make it abundantly clear that software is a major “component” of the system reliability,1 R | Reliability of Computer Systems and Networks Fault Tolerance Analysis and Design Martin L. Shooman Copyright 2002 John Wiley Sons Inc. ISBNs 0-471-29342-3 Hardback 0-471-22460-X Electronic 5 SOFTWARE RELIABILITY AND RECOVERY TECHNIQUES INTRODUCTION The general approach in this book is to treat reliability as a system problem and to decompose the system into a hierarchy of related subsystems or components. The reliability of the entire system is related to the reliability of the components by some sort of structure function in which the components may fail independently or in a dependent manner. The discussion that follows will make it abundantly clear that software is a major component of the system reliability 1 R. The reason that a separate chapter is devoted to software reliability is that the probabilistic models used for software differ from those used for hardware moreover hardware and software and human reliability can be combined only at a very high system level. Section discusses a macrosoftware reliability model that allows hardware and software to be combined at a lower level. Specifically if the hardware software and human failures are independent often this is not the case one can express the system reliability RSY as the product of the hardware reliability RH the software reliability RS and the human operator reliability Ro. Thus if independence holds one can model the reliability of the various factors separately and combine them RSY RH X RS X Ro Shooman 1983 pp. 351-353 . This chapter will develop models that can be used for the software reliability. These models are built upon the principles of continuous random variables 1Another important component of system reliability is human reliability if an operator is involved in any control monitoring input or similar task. A discussion of human reliability models is beyond the scope of this book the reader is referred to Dougherty and Fragola 1988 . 202 INTRODUCTION 203 developed in Appendix A
