![UML use case diagrams graphical notation reference - subject, actor, use cases, relationships between them, extend, include. UML use case diagrams graphical notation reference - subject, actor, use cases, relationships between them, extend, include.](https://www.uml-diagrams.org/use-case-diagrams/use-case-actor-rel-gener.png)
UML use case diagrams graphical notation reference - subject, actor, use cases, relationships between them, extend, include.
![An association between UML actor and a use case indicates that the actor and the use case communicate with each other. An association between UML actor and a use case indicates that the actor and the use case communicate with each other.](https://www.uml-diagrams.org/use-case-diagrams/use-case-association-optional-actors.png)
An association between UML actor and a use case indicates that the actor and the use case communicate with each other.
![A Use Case diagram showing the use cases, actors, and protocols for the... | Download Scientific Diagram A Use Case diagram showing the use cases, actors, and protocols for the... | Download Scientific Diagram](https://www.researchgate.net/publication/220950230/figure/fig1/AS:668936806866957@1536498371306/A-Use-Case-diagram-showing-the-use-cases-actors-and-protocols-for-the-PDMA-In-this.png)
A Use Case diagram showing the use cases, actors, and protocols for the... | Download Scientific Diagram
![Use case diagrams are UML diagrams describing units of useful functionality (use cases) performed by a system in collaboration with external users ( actors). Use case diagrams are UML diagrams describing units of useful functionality (use cases) performed by a system in collaboration with external users ( actors).](https://www.uml-diagrams.org/use-case-diagrams/business-use-case-diagram-elements.png)