In this paper we adopt a component model based on object-oriented systems, introducing the concepts of components and their structure. A component consists of a dynamically changing set of connected objects. Only some of these objects are interface objects, and are thus accessible from the environment. During the component lifetime not only the number of objects, but also that of interface objects, and their connections change. To describe this situation, we introduce Component Interface Diagrams (CIDs) -- an adaption of UML diagrams -- as a notation to characterize interfaces of components, their structure, and their navigability. We show how CIDs can be used to describe the in-house developed Open Editor Framework (OEF). Finally, we give guidelines that allow to map components described with CIDs directly to several component technologies, like ActiveX, CORBA, or Java Beans.