Many Function Point (FP) technique adaptations have been proposed to estimate object-oriented software development projects. However, most research works propose rules to identify FP according previous versions of the FP Counting Practices Manual or they do not include some important UML specifications such as the composition relationship between classes.. In this paper, we present the rules to identify logic files using analysis class diagrams that are included in the UML2FP technique that we have defined, and a software tool named Tupux that support UML2FP application. These rules were defined in accordance with the recommendations included in the FP Counting Practices Manual 4.3.1. We also present the results obtained by applying our rules to software size estimation in a case study performed with undergraduate and graduate students. These results have proved that a person can make mistakes when applying the technique which could be avoided by using a software tool.