System use case diagrams
A system use case diagram displays the relationships between consumers and providers of application services. Application services are consumed by actors or other application services and the application use case diagram provides added richness in describing application functionality by illustrating how and when that functionality is used. The purpose of the system use case diagram is to help to describe and validate the interaction between actors and their roles with applications. As the architecture progresses, the use case can evolve from functional information to include technical realization details. Architectural system use cases can also be re-used in more detailed system design work.
System use case diagrams use UML use cases. TOGAF roles and actors are used in place of UML actors. "Component realization" links enable you to express which application components implement which use cases.
Use cases are enriched by the presentation of the application components that implement them
External actor: An actor that is external to the enterprise.
Internal actor: An actor that belongs to the enterprise.
Communication link: Expresses the communication that takes place between actors and the use case in which they are involved.
Component realization link: Component realization between an application component and the business element that it implements.