The Applicant will be enrolled in the university as a student if they are eligible.ġ.The Applicant has already undergone initial checks to verify that they are eligible to enroll.The Registrar is logged into the system.
The Enroll in University Use Case (narrative style). A condition statement, such as “Condition: Enrollee is an international student,” could have been indicated immediately following the name of the use case but, in this example, it was fairly obvious what was happening.įigure 2. If several use cases extended this one from the same point, then each one would need to be listed. Notice how the identifier and the name of the use case is indicated. The red text in Figure 2 presents an example of how an extension point would be indicated in the basic course of action of the “Enroll In University” use case. This is accomplished through the use of an extension point, which is simply a marker in the logic of a base use case indicating where extension is allowed.
Just as you indicate the point at which the logic of an alternate course replaces the logic of a portion of the basic course of action for a use case, you need to be able to do the same thing for an extending use case. The opportunities for reuse in use-case models. Note, the extending use case¾in this case “Perform Security Check”would list “UC33 Enroll in University,” the base use case, in its “Extends” list.įigure 1. My preference is to use extend dependencies sparingly. Many modelers avoid the use of extend dependencies as this technique has a tendency to make use-case diagrams difficult to understand. I also like to introduce an extending use case whenever I need an alternate course for an alternate course in this case, the extending use case would encapsulate both alternate courses. In fact, a good rule of thumb is you should introduce an extending use case whenever the logic for an alternate course of action is at a complexity level similar to that of your basic course of action. In this case, “Enroll in University” is the base use case and “Perform Security Check” is the extending use case.Īn extending use case is, effectively, an alternate course of the base use case. In the use case diagram of Figure 1 , you see the use case “Perform” extends the use case “Enroll in University,” the notation for doing so is simply a normal use-case dependency with the stereotype of. When the extending use case activity sequence is completed, the base use case continues. This allows an extending use case to continue the activity sequence of a base use case when the appropriate extension point is reached in the base use case and the extension condition is fulfilled. The extending use case accomplishes this by conceptually inserting additional action sequences into the base use-case sequence. Potential reuse can be model through four generalization relationships supported by UML use-case models:Īn extend dependency, formerly called an extends relationship in UML v1.2 and earlier, is a generalization relationship where an extending use case continues the behavior of a base use case. One of your goals during analysis is to identify potential opportunities for reuse, a goal you can work toward as you are developing your use-case model.
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