Separation of concerns [5] plays a critical role to the success of software development and evolution. This paper focuses mainly on an approach to separate concerns during analysis stage. More specifically, concerns are collaborations in a given role-based system [2, 3], and one or more other collaborations to be added due to an incremental change. First, we investigate changes made to an individual object?s behavior by superimposing the refinement on the object?s statechart within a proposed formal dynamic behavior model. Such individual extensions of collaborative objects are then put together in a collaborative context for a holistic effect crosscutting many objects due to the introduction of an incremental change. In addition to behavior model based on statecharts, we claim that modeling a collaborative system requires an extra protocol model which is separate but complementary to the behavior model. We believe that complete behavior of any system, either complete or partial, can be fully expressed by these two models. More importantly, incremental changes and their effects can be easily handled in a modular fashion within these models.