The UML provides use case diagram notation to illustrate the names of use cases, actors, and the relationships between them.
Use case diagrams are usually referred to as behavior diagrams used to describe a set of actions (use cases) that the system can perform in collaboration with one or more external users of the system (actors). Each use case should provide some observable and valuable result to the actors or other stakeholders of the system.
Why Use Case Diagrams?
Use case diagrams are valuable for visualizing the functional requirements of a system that will translate into design choices and development priorities.
Use case diagrams specify how the system interacts with actors without worrying about the details of how that functionality is implemented.
Symbols and Notations
System
Draw your system's boundaries using a rectangle that contains use cases. Place actors outside the system's boundaries.
Use case
Draw use cases using ovals. Label the ovals with verbs that represent the system's functions.
Actors
Actors are the users of a system. It is represented with stick events. When one system is the actor of another system, label the actor system with the actor stereotype.
Relationships
Illustrate relationships between an actor and a use case with a simple line(i.e association). For relationships among use cases, use arrows labeled either "uses" or "extends." A "uses" relationship indicates that one use case is needed by another in order to perform a task. An "extends" relationship indicates alternative options under a certain use case.
Example Use case Diagram for PO
Why Use Case Diagrams?
Use case diagrams are valuable for visualizing the functional requirements of a system that will translate into design choices and development priorities.
Use case diagrams specify how the system interacts with actors without worrying about the details of how that functionality is implemented.
Symbols and Notations
System
Draw your system's boundaries using a rectangle that contains use cases. Place actors outside the system's boundaries.
Draw use cases using ovals. Label the ovals with verbs that represent the system's functions.
Actors are the users of a system. It is represented with stick events. When one system is the actor of another system, label the actor system with the actor stereotype.
Illustrate relationships between an actor and a use case with a simple line(i.e association). For relationships among use cases, use arrows labeled either "uses" or "extends." A "uses" relationship indicates that one use case is needed by another in order to perform a task. An "extends" relationship indicates alternative options under a certain use case.
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