The composition of services and features often leads to unwanted situations, because it is a non-monotonic operation over services and features. When a new service is added to an existing system, conditions have to be checked to ensure that the resulting system satisfies a list of required properties. Following the system approach of Abrial, we develop services and features in an incremental way and use refinement to model the composition of services and features. Proof obligations state the preservation or the non-preservation of properties, namely invariant or more generally safety properties. The method helps us in understanding when a service is interfering with another, and allows us to give multiple views of each service according to the level of its refinement. Finally, we validate our method with the Atelier B tool.