Usecase Diagram – Use Case Diagram – usecase chart – usecase diagrams – use case diagrams. Use case diagram is a simple representation of a user interaction with the system and shows specifications of a use case. Usecase diagrams can show the different types of system users and ways they interact with the system. Usecase diagrams are used in together with the textual use case and will often be used with other types of diagrams. Sample use case diagram. sample usecase diagrams. Example of a usecase diagram. Use case diagrams.