As components, also systems can specify that the offer the functionality of a specific interface or that they require functionality of a specific interface. Analogous to the component roles, the PCM defines system provided and system required roles. The semantics corresponds to the semantics of the roles of a complete component type. The system offers the functionality specified in the provided interfaces if all requirements of the system are met. If they are not met, only a subset will be offered. The semantics of the required interfaces is that a system may call other systems using a required role. It can not call other services than those defined in the system required roles. Using parametric contracts (see section 2.4) for functional dependencies, the actuall demand or the actual provided functionally can be derived (which would result in a system context role, but as it can be fully derived, it is not part of the PCM specifications).