We follow a Virtual Organization (VO) approach for Requirements Engineering (RE) to define and describe the collaborative process needed in a French home care scenario. We use the Intentional level of abstraction for building the models to define the alliance, collaboration and objectives. In this level we identify the intra, inter and extra relationships between the organizations. The approach is illustrated in the context of a French regional project looking for innovative ideas for the care of fragile people within legal, medical, technical and volunteering concerns. Our goal is to facilitate iterative modeling taking into account all organizations' points of view and manage complexity with a top-down refinement.