Use Case Diagram

Use case diagram describes the specification of users and their possible interactions with the system. These possible interactions are called use cases.

Components of a use case diagram

To understand a use case diagram, it is important to first understand its components. Use case diagrams have the following components:

• Actor: Users are called actors. They interact with the system. They could be humans, machines/hardware, or other external systems. There are two types of actors:

  • Primary actors: These are the humans or external systems that interact with that system and are responsible for initiating the use case. They are placed on the left side in a use case diagram. Primary actors are also called active actors.

  • Secondary actors: These are the ones that are used by the system to assist the primary actors in a use case. They cannot interact with the system on their own. They need primary actors to initiate a use case. Secondary actors are also called passive actors, and they are placed on the right side in a use case diagram.

• Use case: This is a single function performed on a system by an actor. It is represented by an oval shape.

• Package: This is a group of different elements. These groups are represented inside a folder icon.

• Note: This is used to add additional information about any component or relationship in a use case diagram.

The representation of the components explained above in a use case diagram is given below: