Use Cases - Finding Use Cases - Subject

6 important questions on Use Cases - Finding Use Cases - Subject

What is the Subject of a Use Case?

The Subject of a Use Case is just the system or system component that offers up these services.

When you first attack a problem, the Subject would be the entire system.

But what is the Subject in large projects?

If your project is large and uses a divide-and-conquer approach, such as decomposition, each subsystem would become a Subject when the work is at the subsystem level.

From the perspective of each subsystem, however, any other communicating subsystem would be an Actor (an external source or sink of information, events, or data).

Therefore, in one model, a model element may be a Subject, but in a different model, the same element may be an Actor, depending on what you are concentrating on for your System of Interest.

Why is the right actor a box ?

Because the External System is not a person, we use the option to employ a stereotyped Class box.

How do we represent the Subject?

In a Use Case diagram, the Subject is a diagram element that is a box with the name in the upper-left corner. An optional stereotype in «» may be placed above the Subject name.

What is an other name for the Subject and why?

Sometimes, we call the Subject the system boundary.
As more than one system can offer up the same

Use Case, a Use Case can appear within multiple System Boundaries.

In Fig. 12.10, we show a metamodel diagram indicating the relationship between Subjects and Use Cases.

What can we conclude from this?

Though it is possible to have a Use Case without a Subject, there is usually at least one Subject for a Use Case

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