What is an actor?

An actor is something that interacts with our system. The actor could be either an external entity such as another system, or a particular role that a user might take. The important bit to remember is that actors represent roles - not individuals. So another way to look at it might be that a particular person could interact with a system in several different ways. Each one of those interactions would be illustrated by the use of an actor.

It is also important to understand what is meant by 'interaction'; each actor must supply a stimulus, or 'do something' to the system, and receive an output in response.

The UML notation for an actor is a stick person, with a short name underneath describing the role. Remember that although it resembles a person, it could also be an external system.

Similarly, several different people might use the system in the same way, so the group of people would be represented by one role or actor.

Knowing that actors are always external to our system means that if we can identify them, we are well on our way to understanding where the system boundary lies.

Quick Question: Which of the following actors are valid?

Review Question

Test your understanding of this topic with the following question:

Think about Tesco online. Word storm all of the possible actors that might want to interact with the system.