What are the various components in sequence diagrams? | UML Interview Questions

=> Actor: Actor represents an external user / end user who interact with the system.
=> Object: Object is represented by one of components of the system.
=> Unit: A unit is a subsystem, or a sub component or other entity within the system.
=> Separator: Separator represents a boundary among sub systems, components or units.
=> Group: Represents different header elements in the subsystem.