1. Basic elements
The elements included in the use case diagram are as follows:
1. Actor
Represents a user, organization, or external system that interacts with your application or system. Represented by a small person.
2. Use Case
A use case is an externally visible system function that describes the services provided by the system. represented by an ellipse.
3. Subsystem
Used to show a part of the function of the system, this part of the function is closely related
4. Relationships
The relationships involved in the use case diagram are: association, generalization, inclusion, and extension.
As shown in the table below:
a. Association
Represents a communication between an actor and a use case, either party can send or receive messages.
【Arrow point】: point to the recipient of the message
b. Inheritance
Inheritance relationship is commonly understood, child use case is similar to parent use case, but exhibits more special behavior; child use case will inherit all the structure, behavior and relationship of parent use case. A child use case can use a piece of behavior from the parent use case or override it. Parent use cases are usually abstract.
【Arrow points】: point to the parent use case
c. Include
Inclusion relationships are used to break down the functionality represented by a more complex use case into smaller steps.
【Arrow pointing】: Point to the decomposed functional use case
d. Extend
The extension relationship refers to the extension of the function of the use case, which is equivalent to providing an additional function for the basic use case.
【Arrow pointing to】: Point to the basic use case
e. Dependency
The above four relationships are standard relationships defined by UML. However, in the use case model diagram of VS2010, a dependency relationship is added, which is represented by a dotted line with an arrow, indicating that the source use case depends on the target use case.
[arrow pointing to]: point to the dependent item
5. Artifact
Although use case diagrams are used to help people understand functional requirements visually, not many people can understand them. In many cases, communicating with users and even using Excel is better than use case diagrams. In VS2010, an element such as "project" was introduced to allow developers to link a common document in the use case diagram.
Use dependencies to depend on a use case on a project:
Then set the Hyperlink of Project->Properties to your document;
This way when you double-click an item on the use case diagram, the associated document will open.
6. Comment
The difference between include (include), extension (extend), and generalization (Inheritance):
Conditional: sub-use cases in generalization and included use cases in include will occur unconditionally, while the occurrence of extended use cases in extend is conditional;
Directness: Sub-use cases in generalization and extension use cases in extend provide direct services to actors, while use cases included in include provide indirect services to actors.
For extend, the extended use case does not contain the content of the base use case, and the base use case does not contain the content of the extended use case.
For Inheritance, a sub-use case contains all the content of the base use case and its relationship to other use cases or actors;
An example use case diagram:
2. Application
1. Open the software and select Empty Project
2. Then find this one in the upper right corner of the open page and right-click Add-->model; then name it model
3. After operation 2, as shown in the figure below
4. Right-click the model (the name you made) and click Add diagram-->use case diagarm, and click as shown below:
6. Now you can start drawing the use case diagram
Reference address: http://www.cnblogs.com/biehongli/p/6052421.html