ODC - Orthogonal Defect Classification

Introduction

Growth modelling, to understand an aspect of software reliability, has several challenges in its use. The published work indicates that there is substantial understanding of its use in the late system test and early field life [8] [10] [4] [3] including the practical aspects of real life data [5]. We also recognize that the use of this as an evaluation tool, does not remove the responsibility of trying to get a better handle of identifying guidelines to improve the process [7]. Our observation, in the practical use of these methods in real development, is that they are usually more successful either in late system test or early field life rather than during the function component test and early system test. Thus, there is a view from the development manager, that professes, that it is rather late in the cycle to realistically do anything significant to correct process problems [2].

Ideally, if reliability growth modelling could be used earlier in the development process, it could provide greater feedback to the management. It is not that it cannot be used - it is just hard. The type of information that can be gleaned from the models is not much better than the use of defect discovery rates that are quite commonly used to determine staffing of testers and fixers. Thus, when there is an increase in the discovery rate beyond nominal values, it kicks off a war room process to determine re-staffing levels and exposures in the ship dates. The question is: can reliability growth models do more than signal alerts - i.e. provide guidance?

This paper proposes a technique that combines Orthogonal Defect Classification (ODC) with growth modelling to provide far greater insight than is commonly available using typical growth models. There are two elements to this insight. One, contributed directly from ODC and the other in combining the relative growth of different groups of defects and projecting them on a common abscissa to make qualitative inferences.

To illustrate these ideas, section 2 of this paper briefly describes ideas of ODC, relevant to the theme of the paper and section 3 describes the qualitative aspects of a typical growth curve. This is done from experience having seen the growth curves developed for several shipped products. Section 4 combines ODC and Growth Modelling and exploits the relative growth to provide causal insight and means to assess risk. Section 5 illustrates these ideas with data from the real world and section 6 provides a summary. This paper should be of interest to the practitioner as well as the theorist, since it opens up a new dimension to measure progress, while there is still an opportunity to take actions and correct the product and process.