Function Point Estimation Methods: a Comparative Overview

The appearance of the Function Point technique has allowed the ICT community to increase significantly the practice of software measurement, with respect to the use of the traditional “Lines of Code approach”. A FP count, however, requires a complete and detailed level of descriptive documentation, like the Functional Specifications of the software system under measurement, to be performed. There are at least two situations in which having an estimation method, compatible but alternative to the standard rules for FP, could be decisive. The first case occurs when the development or enhancement project is in such an early phase that it is simply not possible to perform a FP count according to the IFPUG standards (i.e. in the Feasibility Study). The second case occurs when an evaluation of the existing software asset is needed, but the necessary documentation or the required time and resources to perform a detailed FP calculation are not available. Based on these and other analogous situations, the demand of methods for estimating not counting Function Points has risen from the organizations involved in software business. The technical literature offers several estimation methods that can be examined and compared. This paper presents, therefore, the characteristics of some outstanding methods (Early Function Points, ILF Models, Backfiring) and a general benchmarking model, useful for the evaluation of any additional method, as well.