UML Learning: Use case diagrams

Dragon is the first of ancient Chinese gods, the Legend of the Dragon has nine children, they have their own unique temperament, their respective roles, the benefit of the people. Like our UML, her nine children also have their own unique skills, first of all, today we are going to learn about, use case diagram--the core of nine children, her main function is to describe the user's needs, from the user's perspective to describe the function of the system, pointing out the performer of each function.

In addition, the visualization of systems, subsystems, and system behavior is also demonstrated through use case diagrams, which makes it easier for us to understand the role of these elements. From the point of view of the software engineering and documentation that we learned earlier, use case diagrams are primarily used in the analysis phase, and now we're going to learn the basics of use case diagrams:

Through the above learning, we know that use case diagram is used to describe the needs of users, that is, what the user needs her software, what kind of function, how to realize the value, to bring us what value, and so on. Let's take a look at the properties and granularity and scope of the use case diagram in the next step:

With a simple understanding of the properties of the use case diagram and the scope and granularity of the use case diagram, what is the role of the use case diagram and what problems we need to pay attention to when using a use case diagram: