Application of a usage profile in software quality models

Faults discovered by customers are an important aspect of software quality. The working hypothesis of this paper is that variables derived from an execution profile can be useful in software quality models. An execution profile of a software system consists of the probability of execution of each module during operations. Execution represents opportunities for customers to discover faults. However, an execution profile over an entire customer-base can be difficult to measure directly. Deployment records of past releases can be a valuable source of data for calculating an approximation to the probability of execution. We analyze a metric derived from deployment records which is a practical surrogate for an execution profile in the context of a software quality model. We define usage as the proportion of systems in the field which have a module deployed. We present a case study of a very large legacy telecommunications system. We developed models using a standard statistical technique to predict whether software modules will have any faults discovered by customers on systems in the field. Static software product metrics and usage were independent variables. The significance levels of variables in logistic regression models were analyzed, and models with and without usage as an independent variable were compared. The case study was empirical evidence that usage can be a significant contributor to a software quality model.