UML use case diagram

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.Participant)

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.Link

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

E. Dependency)

The above four relationships are the standard relationships defined by UML. However, dependency is added in the use case model diagram of vs2010, which is expressed by a dotted line with arrows, indicating that the source use case depends on the target Use Case.

[Arrow pointing]: pointing to the dependent item

5. Project (artifact)

Although the use case chart is used to help people understand functional requirements visually, few people can understand it. Many times, it is better to communicate with users or even use Excel than the use case diagram. vs2010 introduces an element such as "project", so that developers can link a common document in the use case diagram.

Dependencies are used to dependencies a use case to a project:

Set the hyperlink of the project-"attribute to your document;

In this way, when you double-click a project in the use case diagram, the associated documents will be opened.

6. Comment)

 

Include), Extended (extend), Generalization (inheritance) Differences:

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 extend, 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 inheritance, subuse cases include all the content of the basic use case and its relationship with other use cases or participants;

Example of a use case chart:

 

Complaints:

I feel that the use case diagram is not mature enough to express the requirements of the system. Users without a UML background almost do not know what to draw.

Second, the arrow symbols that contain links and extended relationships are actually the same arrows. They are differentiated by writing a text above. If they are translated into other languages, they almost do not know what they mean. It is hard to understand why the arrow orientation of the extended relationship refers to the base use case instead of the extended use case.

The "project" element added by vs2010 is a great innovation. It can be associated with documents such as Word and Excel in the use case diagram. But why not integrate these functions directly into the use case? Double-click the use case to bring up a document, which is not easy to understand. It is necessary to add a component to provide a link function.

Use case description table:

In view of the fact that the column chart cannot clearly express the functional requirements, developers usually use a descriptive table to supplement some use cases that are not easy to express. The table provides a reference for everyone: