foreword
The use case diagram is used to describe the user's needs, and it is the first step from the software requirements analysis to the final realization. It describes how people want to use a system. It describes the requirements for a software product from the user's point of view rather than the developer's point of view.
Detailed explanation
have what
use case; actor; relationship between the two (association, generalization, inclusion, extension)
relation
1. Association (line with arrow)
2. Generalization (inheritance, solid line with hollow arrow, the direction of the arrow points from the child use case to the parent use case)
3. Inclusion (the base use case contains the containing use case, the base use case can see the containing use case, And depends on the execution result of the included use case. But the two cannot access each other's properties)
4. Extension (the execution of the basic use case will not involve the behavior of the extended use case, if a specific condition occurs, the behavior of the extended use case will be executed, and then continue )
Granularity – degree of granularity
There is no standard setting for granularity, as long as it conforms to the UML specification, meets user needs, and is easy to understand, it is acceptable.
Too fine granularity Moderate granularity
example
Summarize
The use case diagram is the first diagram we draw, drawn at the requirements stage, and lays the foundation for future work.