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Actors are not part of the systemthey represent anyone or anything that must interact with the system. An actor may
Typically, these actors are found in the problem statement and by conversations with customers and domain experts. The following questions may be used to help identify the actors for a system:
In the UML, an actor is represented as a stickman, as shown in Figure 3-1.
Figure 3-1. UML Notation for an Actor
What Constitutes a "Good" Actor?
Care must be taken when identifying the actors for a system. This identification is done in an iterative fashionthe first cut at the list of actors for a system is rarely the final list. For example, is a new student a different actor than a returning student? Suppose you initially say the answer to this question is yes. The next step is to identify how the actor interacts with the system. If the new student uses the system differently than the returning student, they are different actors. If they use the system in the same way, they are the same actor.
Another example is the creation of an actor for every role a person may play. This may also be overkill. A good example is a teaching assistant in the ESU Course Registration System. The teaching assistant takes classes and teaches classes. The capabilities needed to select courses to take and to teach are already captured by the identification of functionality needed by the Student and the Professor actors. Therefore, there is no need for a Teaching Assistant actor.
By looking at the identified actors and documenting how they use the system, you will iteratively arrive at a good set of actors for the system.
Actors in the ESU Course Registration System
The previous questions were answered as follows :
Based on the answers to the questions posed, the following actors have been identified: Student, Professor, Registrar, and the Billing System.
CREATING ACTORS IN RATIONAL ROSE
The Browser view of the actors for the ESU Course Registration System is shown in Figure 3-2.
Figure 3-2. Actors
A brief description for each actor should be added to the model. The description should identify the role the actor plays while interacting with the system.
The actor descriptions for the ESU Course Registration System are:
DOCUMENTING ACTORS IN RATIONAL ROSE
The documentation for the Student actor is shown in Figure 3-3.
Figure 3-3. Student Actor Documentation
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