Component diagram is used to show how the components of a systems are structurally related to each other. There has been a change in the notation of a component in UML 1.1 as compared to UML 2.0. In UML 1.1, files, DLLs, Jar files etc were also treated as components. This, in a way, was a little confusing as the original idea of a component was something that encapsulates a behavior and has a well defined interface. In UML 2.0, the definition of a component has become more clearer and sharper. In UML 2.0, they are strictly logical and design-time only constructs.
