During the last two decades the software evolution community has intensively tackled the software merging issue whose main objective is to merge in a consistent way different versions of software in order to obtain a new version. Well established approaches, mainly based on the dependence analysis techniques, have been used to bring suitable solutions. These approaches concern the source code or software architectures. However, these solutions are more expensive due to complexity and size of software. In this paper, we overcome this problem by operating at a high level of abstraction. The objective is to investigate software merging at the level of UML activity diagrams, a new interesting issue rather than source code or architectures. Proposed approach, based on dependence analysis techniques, is illustrated through an appropriate case study.