Early Function Points: some practical experiences of use

Due to the wider use of Function Point metrics in the software management field, there is an increasing need for methods to estimate, at an early stage of the software life cycle, a software application’s value in Function Points. This work describes how to use the Early Function Points method (presented at IFPUG 97, Scottsdale, September 97) from the practical point of view and it presents a set of very encouraging project results. Early Function Points are not a measurement alternative to IFPUG 4.0 Function Points, but only a fast and early estimate thereof. The method is based on identifying software objects, like logical data and functionalities provided by the software under evaluation, at different levels of detail. The key factors are: macrofunctions, functions, microfunctions, functional primitives and logical data items. Each of these objects may be assigned a set of FP values based on a statistical table. The approach presented here has proved quite effective in providing a response within ± 10% of the real FP value in most cases. This work shows how to derive the EFP measurement from a set of concise requirements, and compares the EFP forecast with the corresponding actual IFPUG 4.0 FP value. More than 20 project results (both IFPUG counts and EFP estimates) are presented.