Convertibility of Functional Size Measurements: New Insights and Methodological Issues

Objective: Most of the models and tools currently used for effort estimation require in input the measure of the functional size of the program to be developed. In particular, Function Points (FP) are most often used for estimation purposes. However, several organizations are considering to move from Function Point Analysis (FPA) to the COSMIC functional size measurement method, mainly because the latter is more easily and generally applicable than FPA. However, moving from FPA to COSMIC implies that the experience bases funded on function points become unusable. This paper explores the quantitative relations between FPA and COSMIC measures and elements, in view of the transformation of FP into COSMIC Function Points (CFP) and vice versa. Methods: The paper considers the data from 25 projects and analyses the relations that link the basic functional components (BFC) of FPA and COSMIC. With respect to previous studies that addressed only the relations between the different functional size measures, the paper investigates the dependencies of FP and CFP from both FPA and COSMIC basic functional components. Results: In all the examined cases it was found that strong correlations exist between the considered measures. Conclusions: The results found tend to suggest that in presence of a set of projects that are quite homogeneous –with respect to the application domain, the nature of computation performed, and the implementation technology– it is possible to obtain fairly precise estimations of the functional size (expressed either in FP or in CFP) on the basis of a few BFC