Is a description of a series of operations performed by the system (including its variants) in order to produce observable result values for the participants who perform the operations. For example, if you use a calculator, you can think of it as a use case. The participant is Dengfeng, Dengfeng presses 3+3 (the sequence of use case execution), and the calculation machine returns the result 6.

2. Actor

Participants are not people, but the roles they play when using or interacting with the system outside the system. Therefore, participants can be people, things, time or other systems and so on. It should also be noted that the participants are not people or things themselves, but the roles that people or things played at that time. For example, Xiao Ming is a librarian in the library. He participated in the interaction of the library management system. At this time, he can participate in the management as an administrator or borrow books from the library as a borrower. Here Xiao Ming plays two roles, two different participants. Participants are represented by simple figure paintings, and the names of participants are attached below the figures.

Step 3 generalize

Generalization is the same as generalization in a class. A child use case inherits the behavior and meaning of the parent use case, and can also add or override the behavior of the parent use case. A child use case can appear anywhere the parent use case appears (both the parent use case and the child use case have concrete instances). Here are two diagrams to illustrate the concept and meaning of generalization.

4.& lt& lt uses & gt& gt

& lt& lt uses & gt& gt a use case whose relationship is very similar to a function call or a subprocess used in this way, which is called extraction.

Like a use case, it must be used by other use cases because it cannot exist alone. Please look at the picture below.

5.& lt& lt includes & gt& gt

How to explain this definition? Let's explain its function.

Well, the definition is known. Let's use an example to deepen your impression. If there is a personnel system, the manager can view employee information, and can add, modify and delete it, but every time these three operations are performed, the corresponding employee must be located, that is, the employee to be operated must be queried first. Figure 5 shows the use case diagram of this expression, please understand.

6.& lt& lt Extension & gt& gt

& lt& lt Extension & gt& gt It provides a way to add new behaviors to existing use cases. The basic use case provides a set of extension points, which are hooks, and new behaviors can be added to the hooks. The extension use case provides a set of insertion fragments, which can be inserted into the hook position of the basic use case. It should be noted that the base use case does not know any details of the extended use case, and it only provides a hook for the extended use case. This is the same as

7. Use case description

Of course, the use case description is a literal description of the use case. I won't say more about the specific projects to be described here. Let me give you a concrete example, which is clear at a glance. If there is a tutor network, the following is just an abstract fragment. Mainly to explain the meaning of use case description.