To identify an actor, search in the problem statement for business terms that portray roles in the system. An actor is shown as a stick figure in a use case diagram depicted 'outside' the system boundary, as shown in the below figure. If an entity does not affect a certain piece of functionality that you are modeling, it makes no sense to represent it as an actor. But it is up to you to consider what actors make an impact on the functionality that you want to model. Similarly, the person who provides service at the counter is also an actor. For example, for modeling a banking application, a customer entity represents an actor in the application. An actor in a use case diagram interacts with a use case. The different roles the actor represents are the actual business roles of users in a given system. Actors: An actor portrays any entity (or entities) that perform certain roles in a given system.Let us take a closer look at use at what elements constitute a use case diagram. A use case diagram is quite simple in nature and depicts two types of elements: one representing the business roles and the other representing the business processes. Use cases are created when the requirements of a system need to be captured. Normally, domain experts and business analysts should be involved in writing use cases. A use case diagram captures the business processes carried out in the system.
