A Convertibility Study on the Conversion between FPA and COSMIC for Real Time Systems

Function Point Analysis (FPA) measurement method was proposed primarily to measure the functional size of management information systems. The method has been criticized as an inadequate method to measure the functional size of Real Time (RT) applications. Many extensions have been made to the original method to extend its applicability to size RT applications. The Common Software Measurement International Consortium (COSMIC) designed COSMIC function point measurement method to meet the requirement of measuring a wider scope of software domains, particularly, RT applications. This paper aims to derive a convertibility equation between the two methods for small-size RT applications. A systematic conversion approach was applied using two types of conversion (using the unadjusted FPA size and transaction functions size) using 13 small-size RT applications, considering the quality of requirements, via linear and non-linear regression models. The results show that RT applications have a varied functional size for processes, in which FPA method could not quantify it adequately, mainly because of the FPA weighting system tables and the inadequate representation of data files. Moreover, the results show that there is a significant correlation between the two methods, but the conversion factor is slightly larger than the previous studies, in which the conversion factor is more than 1. However, some limitations of FPA method rules relative to RT applications cast some doubts on the possibility to extend the conversion for larger applications size.