A Comprehensive Evaluation of Conversion Approaches for Different Function Points

Abstract: Context: Software cost and effort estimation are important activities for planning and estimation of software projects. One major player for cost and effort estimation is functional size of software which can be measured in variety of methods. Having several methods for measuring one entity, converting outputs of these methods becomes important. Objectives: In this study we investigate different techniques that have been proposed for conversion between different Functional Size Measurement (FSM) techniques. We addressed conceptual similarities and differences between methods, empirical approaches proposed for conversion, evaluation of the proposed approaches and improvement opportunities that are available for current approaches. Finally, we proposed a new conversion model based on accumulated data. Methods: We conducted a systematic literature review for investigating the similarities and differences between FSM methods and proposed approaches for conversion. We also identified some improvement opportunities for the current conversion approaches. Sources for articles were IEEE Xplore, Engineering Village, Science Direct, ISI, and Scopus. We also performed snowball sampling to decrease chance of missing any relevant papers. We also evaluated the existing models for conversion after merging the data from publicly available datasets. By bringing suggestions for improvement, we developed a new model and then validated it. Results: Conceptual similarities and differences between methods are presented along with all methods and models that exist for conversion between different FSM methods. We also came with three major contributions for existing empirical methods; for one existing method (piecewise linear regression) we used a systematic and rigorous way of finding discontinuity point. We also evaluated several existing models to test their reliability based on a merged dataset, and finally we accumulated all data from literature in order to find the nature of relation between IFPUG and COSMIC using LOESS regression technique. Conclusions: We concluded that many concepts used by different FSM methods are common which enable conversion. In addition statistical results show that the proposed approach to enhance piecewise linear regression model slightly increases model’s test results. Even this small improvement can affect projects’ cost largely. Results of evaluation of models show that it is not possible to say which method can predict unseen data better than others and it depends on the concerns of practitioner that which model should be used. And finally accumulated data confirms that empirical relation between IFPUG and COSMIC is not linear and can be presented by two separate lines better than other models. Also we noted that unlike COSMIC manual’s claim that discontinuity point should be around 200 FP, in merged dataset discontinuity point is around 300 to 400. Finally we proposed a new conversion approach using systematic approach and piecewise linear regression. By testing on new data, this model shows improvement in MMRE and Pred(25).