Modern Information and Communication Technology open a door for innovations that can improve the functioning of companies. Many innovations can come from the analysis of business processes. Today modeling is widely used for the analysis of business processes. In these work we propose a process modeling technique based on role modeling. To specify a process where one business object may play several roles, a synthesis operation (the composition of two base roles in a third role) has to be specified. All role-based techniques have difficulties specifying role synthesis: synthesis is never specified without the description of actual messages passing between business roles. Such implementation details complicate the understanding of the model and semantics of synthesis become implicit. To specify a business process of a complex system at a higher level of abstraction requires the proper understanding of relationships between roles, when they are put together in one common context. In this paper we define the concept of synthesis constraints that shows relations between roles. Using synthesis constraints allows a business modeler to make explicit his decisions about how the synthesis is done in an abstract and implementation independent way. This approach can be used for building a BPR case tool that enables the discovery of new business processes by means of different disassembling and assembling of roles.