Use case diagrams describe interactions between actors and a system to accomplish goals. A use case diagram typically includes: 1) Actors that interact with the system from outside, such as users or other systems. Common actor types are primary actors whose goals are fulfilled by the system and supporting actors that provide services. 2) Use cases that represent functions or tasks performed by the system. They are connected to relevant actors and may have relationships like include and extend. 3) Relationships between use cases like include, which shows a use case incorporating another, and extend, where a use case optionally extends another. Use case diagrams provide an overview of a system's functions and how outside actors interact with them at a