Components are elements in the implementation model and are used to express the way the system is implemented in a set of smaller " chunks ." Components offer one or more interfaces and are dependent only on the interfaces of other components. Using components lets you design, implement, deliver, and replace various parts of the system independently of the rest of the system. The design model element that corresponds to the component is the subsystem: Subsystems are independent units of functionality that allow different parts of the system to be designed and implemented independently. Subsystems offer interfaces and are dependent on the interfaces of other model elements. If necessary, the design can also include a data model ( expressed in UML) that expresses the way the persistent objects in the system are stored and retrieved. A data model is useful when the underlying database technology imposes a significantly different physical model from that of the object-oriented application. |