Software Reliability Modeling

1 Introduction This chapter proposes an overview of some aspects of Software Reliability (SR) engineering. Most systems are now driven by software. So that, it is well-recognized that assessing reliability of software applications is a major issue in reliability engineering, particularly in terms of cost. But predicting software reliability is not easy. Perhaps the major difficulty is that we are concerned primarily with design faults which is a very different situation from that tackled by the conventional hardware theory. A fault (or bug) refers to the manifestation in the code of a mistake made by the programmer or designer with respect to the specification of the software. Activation of a fault by an input value leads to an incorrect output. Detection of such an event corresponds to an occurrence of a software failure. Input values may be considered as arriving to the software randomly. So although software failure may be not generated stochastically, it may be detected in such a manner. Therefore, this justifies the use of stochastic models of the underlying random process that governs the software failures. We briefly recall in Section 2, basic concepts of stochastic modeling for reliability. Two approaches are used in SR modeling. The prevalent is the so-called black-box one, in which only the interactions of the software with the environment are considered. Following [1] and [2], we use in Section 3 the self-exciting point processes as basic tool to model the failure process. That enables an overview of most of published SR models. A second approach, called the white-box one, incorporates in models, information on the structure of the software. This is presented in Section 4. Section 5 proposes basic techniques for calibrating black-box models. The last section tries to give an account for the current practices in SR modeling and to point out some challenging issues for future research. Note that this chapter does not aspire to cover the whole topic of SR engineering. In particular , we do not discuss: fault prevention, fault removal, fault tolerance which are three methods to achieve reliable software. We focus here on methods to forecast failure times. For a more complete view, we refer to [3], the handbooks [4] and [5]. We have used the two recent books [2] and [6] to prepare this chapter. We also recommend to read the short paper [7], that describes, in particular, the available software reliability toolkits (with additional …