Building high-quality software fault predictors

Over the past several years, we have been developing software fault predictors based on a system's measured structural evolution. We have previously shown significant linear relationships between code churn, a set of synthesized metrics, and the rate at which faults are inserted into the system in terms of number of faults per unit change in code churn. A limiting factor in this and other such investigations has been the absence of a quantitative, consistent and repeatable definition of what constitutes a fault. The rules for fault definition were not sufficiently rigorous to provide unambiguous, repeatable fault counts. Within the framework of a space mission software development effort at the Jet Propulsion Laboratory we have developed a standard for the precise enumeration of faults. This new standard permits software faults to be measured directly from configuration control documents. We compared the new method of counting faults with two existing techniques to determine whether the fault-counting technique has an effect on the quality of the fault models constructed from those counts. The new fault definition provides higher quality fault models than those obtained using the other definitions of fault. Copyright (C) 2006 John Wiley & Sons, Ltd.