Use case diagram (usecase di#)-UML diagram (1)

 

From the above use case diagram model, we can get a general idea of what the use case diagram describes. The following is a detailed introduction.

 

The use case diagram is used to describe what roles can do through a certain system. The use case diagram focuses on the external performance of the system, the interaction between the system and people, and the interaction between the system and other systems.

The use case diagram has three elements: Role, use case, and relationship.

1. Role (actor): it refers to the roles used in the system. Different roles use different system functions, which are represented by the villain in the use case diagram.

It is worth noting that the role may be a person or not a person, but another system. If the system interacts with another system, you can draw another system as a role.

The principle of role analysis can also be seen as what we need to think about when getting a role:

1) who directly use the system?

2) maintenance personnel involved

3) peripherals used

4) Other connected systems

5) What other people and things are interested in the results of this system.

 

2. Use Case: this is a function of the system. It is represented in an elliptical circle in the use case diagram and described in text in the circle. It is generally a moving object phrase.

It is worth noting that a use case does not necessarily belong to only one role. Some use cases belong to multiple roles at the same time, that is, they are "shared" by multiple roles ".

 

Here, the library information system describes the granularity and scope of use cases.

Overview level

 

 

User target level

 

 

Sub-function level

 

 

3. relationship: the relationship between the role and the use case. lines are used in the use case diagram,

A line refers to a line between a role and a use case. These lines are used to connect a role (villain) and a use case (circle), indicating what use cases a role can "do.

 

There are two types of lines: those without arrows and those with arrows.

A line with arrows indicates the flow of data during the interaction between the role and the system. If the arrow points to a use case, the role needs to input data to the system. If the arrow points to the role, the system outputs data to the role. If there are no arrows, the data flow is not clearly indicated.

 

Sometimes, when the use case chart is refined to the sub-function level, a dotted line arrow appears, as shown in.

 

To sum up, and combine the details that need to be paid attention to when drawing the use case diagram, sort out the following figure to illustrate the use case diagram more vividly.