A fuzzy logic based set of measures for software project similarity: validation and possible improvements

The software project similarity attribute has not yet been the subject of in-depth study, even though it is often used when estimating software development effort by analogy. Among the inadequacies identified (M. Shepperd et al., 1996; 1997) in most of the proposed measures for the similarity attribute, the most critical is that they are used only when the software projects are described by numerical variables (interval, ratio or absolute scale). However, in practice, many factors which describe software projects, such as the experience of programmers and the complexity of modules, are measured in terms of an ordinal (or nominal) scale composed of qualifications such as `low´ and `high´. To overcome this limitation, we propose a set of new measures based on fuzzy logic for similarity when the software projects are described by categorical data. The proposed measures are validated by means of an axiomatic validation approach. We also present the results of an empirical validation of our similarity measures, based on the COCOMO´81 database