Function Point: how to transform them in effort? This is the problem!
Gianfranco Lanza · 2008
The need to estimate the effort and, consequently, the cost of a software project is one of the most important issues in ICT world. The use of function point to measure the functional dimension of a software project is the base in CSI Piemonte for deriving the effort and consequently the cost. If the process to measure the functional dimension in function point can be considered as a scientific method, based on rules defined in IFPUG Function Point Counting Practice Manual, the process to determine the effort is not so deterministic and scientific but it is depending on many non functional or technical factors. In CSI Piemonte it has been developed a model to determine the effort by Function Point through a process that, step by step, takes into account many possible technical factors that can influence the productivity. • The first step is to determine the “medium productivity” about the project through two parameters: the programming language (according to Capers Jones Programming Language Table [1] or ISBSG Repository [2]) and the functional dimension in Function Point (the productivity decrease if the dimension of the software project arises). • The second step is to analyse the Technical Factors (algorithmic complexity, relations with other applications, with other projects, time binding, etc.) that influence the productivity: in accord to a nominal value they can arise, reduce or not modify the “medium productivity”. • The Third step is to take into account the risks of the project, expressed as a contingency: an additional percentage of the total effort calculated as a multiplication of the probability that the risk happens and its relative impact on the project. • The Fourth step is to consider other activities, not depending by the dimension of the project, but worthwhile in calculating the effort (for example to develop a prototype to evaluate a new technology). At the end the total effort is divided into RUP Activities for a better scheduling of the project, in according to top down estimate technique. The effort estimate derived by Function Point has to be compared with the effort estimate derived by experience, thus it’s not the only method used to estimate effort and cost.