Product metrics for object-oriented systems

We survey metrics proposed for object-oriented systems, focusing on product metrics. The survey is intended for the purposes of understanding, classifying, and analyzing ongoing research in object-oriented metrics. The survey applies fundamental measurement theory to artifacts created by development activities. We develop a mathematical formalism that captures this perspective clearly, giving appropriate attention to the peculiarities of the object-oriented system developmenr process. Consistent representation of the available metrics, following this mathematical formalism, shows that current research in this area contains varying coverage of different products and their properties at different development stages. The consistent representation also facilitates several analyses including aggregation across metrics, usage across metrics, equivalent formulation of metrics by multiple researchers, and exploitation of traditional metrics for object-oriented metrics. We also trace the chronological development of research in this area, and uncover gaps that suggest opportunities for future research.