In commercial software development organizations, increased complexity of products, shortened development cycles, and higher customer expectations of quality have placed a major responsibility on the areas of software debugging, testing, and verification. As this issue of the IBM Systems Journal illustrates, there are exciting improvements in the underlying technology on all three fronts. However, we observe that due to the informal nature of software development as a whole, the prevalent practices in the industry are still immature, even in areas where improved technology exists. In addition, tools that incorporate the more advanced aspects of this technology are not ready for large-scale commercial use. Hence there is reason to hope for significant improvements in this area over the next several years. Since one of the goals of this special issue of the IBM Systems Journal is to be accessible to the students of software engineering at large, we define relevant terminology and its implications (we include formal no

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Defect-occurrence projection is necessary for the development of methods to mitigate the risks of software defect occurrences. In this paper, we examine user-reported software defectoccurrence patterns across twenty-two releases of four widelydeployed, business-critical, production, software systems: a commercial operating system, a commercial middleware system, an open source operating system (OpenBSD), and an open source middleware system (Tomcat). We evaluate the suitability of common defect-occurrence models by first assessing the match between characteristics of widely-deployed production software systems and model structures. We then evaluate how well the models fit real world data. We find that the Weibull model is flexible enough to capture defect-occurrence behavior across a wide range of systems. It provides the best model fit in 16 out of the 22 releases. We then evaluate the ability of the moving averages and the exponential smoothing methods to extrapolate Weibull model parameters using fitted model parameters from historical releases. Our results show that in 50% of our forecasting experiments, these two naïve parameterextrapolation methods produce projections that are worse than the projection from using the same model parameters as the most recent release. These findings establish the need for further research on parameter-extrapolation methods that take into account variations in characteristics of widely-deployed, production, software systems across multiple releases.

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Defect-occurrence projection is necessary for the development of methods to mitigate the risks of software defect occurrences. In this paper, we examine user-reported software defectoccurrence patterns across twenty-two releases of four widelydeployed, business-critical, production, software systems: a commercial operating system, a commercial middleware system, an open source operating system (OpenBSD), and an open source middleware system (Tomcat). We evaluate the suitability of common defect-occurrence models by first assessing the match between characteristics of widely-deployed production software systems and model structures. We then evaluate how well the models fit real world data. We find that the Weibull model is flexible enough to capture defect-occurrence behavior across a wide range of systems. It provides the best model fit in 16 out of the 22 releases. We then evaluate the ability of the moving averages and the exponential smoothing methods to extrapolate Weibull model parameters using fitted model parameters from historical releases. Our results show that in 50% of our forecasting experiments, these two naïve parameterextrapolation methods produce projections that are worse than the projection from using the same model parameters as the most recent release. These findings establish the need for further research on parameter-extrapolation methods that take into account variations in characteristics of widely-deployed, production, software systems across multiple releases.