Use case diagram of UML

As mentioned in the previous article on the relationship in the use case diagram, the use case diagram describes user requirements, describes system functions from the user's perspective, and points out the executors of various functions, emphasizing who is using the system, which functions are implemented by the system executor.

Roles, relationships, and use case relationships

The basic elements of a use case diagram are use cases, roles, and relationships. The relationships are described in detail in the relationships in the use case diagram.

Role

The role of use cases not only refers to people, but also includes some things, such as other systems connected to the system, system peripherals, etc, the role mainly serves to interact with the system, input the system, and accept the system information.

When we draw a Use Case chart, we sometimes hesitate how the actor (role) gets it. There are several principles for recognizing the actor:

1. Who uses the system?

2. Who needs system support?

3. Who maintains the relational system?

4. What hardware does the system need to operate?

5. other systems that need to interact with the system

6. persons or things interested in the results of the system

For a good use case, the use case should be named from the executor's perspective, and the system boundary should be clearly defined. The size and description of the use case meet the requirements, which is simple and not chaotic, there are not too many use cases. At the same time, the use cases can make users understand their meaning accurately. Granularity and range granularity use cases are used to describe the size of user targets. The user granularity is divided into three levels: Overview level: business target user level: the user uses the system's target sub-function level: the specific user Target scope is to talk about the user's goal: overview-level Use Case Scope: entire enterprise user target-level Use Case Scope: system boundary-level sub-function-level Use Case Scope: a sub-system or a component, such as a data room charging system, enables students to manage on/off a card: Overview level: user target level: sub-function level: Data room charging system use case diagram: