Model transformations form a key part of MDA (Model-Driven Architecture). Most of the studies deal with the transformations from PIM (Platform-Independent Model) to PSM (Platform-Specific Model) and PSM to Code, but very few deal with the transformation from CIM (Computation-Independent Model) to PIM. This last transformation usually depends on business analysts’ and software architects’ experience and creativity. This paper proposes a disciplined approach to transform a CIM into a PIM. It first uses UML2 activity diagrams to model the business processes up to the users’ tasks. The activity diagrams are then detailed to specify the system requirements. The system components are directly deduced from the requirement model elements. Finally, a set of business archetypes helps??detail the system components to yield the PIM. The same approach applies equally to CIM and PIM built to model inter-enterprise processes and systems. A case study illustrates our approach. It demonstrates how it reinforces the components traceability and reusability and how it globally improves the modeler’s efficiency. Furthermore, the use of the activity diagrams, as a single technique to build business process and requirement models, is an important facilitator which prepares our further work to automate this approach.