How to Find Actors for Use Case Diagram

 How to Find Actors for Use Case Diagram?

When working from an Action/Response table, identifying the actors is easy: entities whose behaviour appears in the "Actor's Actions" column are the actors, and entities whose behaviour appears in the "System's Response" column are components in the system.

If you are working from an informal narrative, a sequence diagram, or a scenario description, the actors are typically those entities whose behaviour cannot control or change (i.e., agents that are not part of the system that you are building or describing.) The most obvious candidates for actors are the humans in the system. Except in rare cases when the system you are describing is actually a human process, such as a specific method of dealing with customers that employees should follow, the humans that you must interact with will all be actors.

If your system interacts with other systems (databases, servers maintained by other people, legacy systems) you will be best to treat these as actors, also, since it is not their behaviour that you are interested in describing.