Actor Reference –

Definition:
An actor reference is a usage instance of an actor within another actor class in a structure diagram. It allows you to define how one actor (component) is composed of or interacts with others.

Key Characteristics:

• Used Inside Actor Classes:
  Actor references can only appear inside an actor class (i.e., they are used to define the internal structure of a complex actor in a hierarchical way).
• Represents a Component or Sub-Actor:
  Each actor reference represents a sub-component (another actor) that helps form the complete behaviour of the enclosing actor.
• Reference Ports on Outside Border:
  Actor references can have reference ports (connectors) on their border, allowing them to communicate with other actors or the environment through defined interfaces.

Analogy / Simplified View:

If an actor class is like a circuit board, then actor references are like the individual chips or components placed on the board — each serving a specific role and interacting via ports (pins)