Glossary · Systems engineering and MBSE
Use case diagram
German: Anwendungsfalldiagramm
In SysML and UML, a use case diagram is a behavior diagram that shows the functionality a system provides (use cases) and the actors, such as people or external systems, that interact with it.
- Systems engineering
In one sentence
A use case diagram shows the functions a system offers and the actors, people or external systems, that use them.
Example
The use case diagram of a machine shows the operator starting production, the setter changing formats, the maintenance technician performing lockout and the MES downloading orders.
How it applies
- Engineering: Use case diagrams capture scope early and connect stakeholders to the functions they need; they often follow from the Concept of operations (ConOps).
- Safety: Listing all actors and use cases, including maintenance and cleaning, supports the identification of Intended use and tasks for the risk assessment.
- Documentation: Actors map to target groups and use cases to task topics; the documentation team can use the diagram to plan manuals per role.
- Scope control: Use cases outside the system boundary or explicitly excluded should be noted, since excluded tasks are relevant for foreseeable misuse and for the limits stated in the manual.
Use case diagram vs. activity diagram
A use case diagram shows what functions exist and who uses them, but not how they run. The steps of a use case are described in an Activity diagram or Sequence diagram.