Use case diagram of UML

The use case diagram is used to describe the relationship between users, requirements, and system functional units. It shows a system function model diagram that can be observed by external users.

[PURPOSE]: help the development team understand the functional requirements of the system in a visual manner.

The use case diagram contains the following elements:

1. Participants)

The user, organization, or external system that interacts with your application or system. Represented by a villain.

2. Use Case)

Use Cases are externally visible system functions that describe the services provided by the system. It is represented by an ellipse.

3. Subsystem)

It is used to display some functions of the system. These functions are closely related.

4. Relationship

The relationships in the use case diagram include association, generalization, inclusion, and extension.

See the following table:

A. Association)

Communication between participants and use cases. Any Party can send or receive messages.

[Arrow pointing]: pointing to the Message Receiver

B. Generalization)

It is generally understood as an inheritance relationship. Child cases are similar to parent cases, but show more special behaviors. Child Cases inherit all structures, behaviors, and relationships of the parent case. A child use case can use a behavior of the parent use case or reload it. The parent case is usually abstract.

[Arrow pointing]: pointing to the parent use case

C. Include)

The include relation is used to break down the Functions Represented by a complex use case into smaller steps.

[Arrow pointing]: points to the decomposed functional use cases.

D. Extended (extend)

Extended relationship refers to the extension of the use case function, which is equivalent to providing an additional function for the basic use case.

[Arrow pointing]: pointing to basic Use Cases

Include, extended, and inheritance:

Conditional: The child use cases in generalization and the contained use cases in include occur unconditionally, while the extended use cases in extend are conditional;

Directness: subuse cases in generalization and extended use cases in extend provide direct services for participants, while included use cases provide indirect services for participants.

For expansion, the extended use case does not contain the content of the basic use case, and the basic use case does not contain the content of the extended use case.

For generalization, A subuse case contains all the content of the basic use case and its relationships with other use cases or participants;

Example of a use case chart:

Original article: http://blog.csdn.net/tianhai110/article/details/6369762

Use case diagram of UML