UML Modeling use case diagrams

Use case diagrams are primarily used to describe the relationship between users, requirements, and system functional units. It shows a model diagram of a system function that an external user can observe.

"Purpose": helps the development team to understand the functional requirements of the system in a visual way.

The use case diagram contains the following elements:

1. Participant (actor)

Represents a user, organization, or external system that interacts with your application or system. With a villain.

2. Use Cases

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

3. Subsystems (Subsystem)

Used to show a part of the system function, this part of the function is closely related.

4. Relationship

The relationships involved in a use case diagram are: Association, generalization, inclusion, and extension.

As shown in the following table:

A. Association (association)

Represents the communication between a participant and a use case, and either party can send or accept a message.

Arrow point to: Point to the message receiver

B. Generalization (inheritance)

Is the commonly understood inheritance relationship, where the child use case is similar to the parent use case, but behaves more specifically, and the child use case inherits all the structures, behaviors, and relationships of the parent use case. A child use case can use a section of the parent use case, or it can be overloaded. The parent use case is usually abstract.

Arrow pointing to: pointing to the parent use case

C. Include (include)

　　The include relationship is used to break down the functionality represented by a more complex use case into smaller steps.

"Arrow pointing": pointing to decomposed function use cases

D. Extensions (Extend)

An extension relationship is an extension of a use case feature, which is equivalent to providing an additional function for the underlying use case.

Arrow pointing to: pointing to the underlying use case

E. Dependency (Dependency)

The above 4 relationships are standard relationships defined by UML. However, in the VS2010 use case Model diagram, a dependency is added, represented by a dashed line with arrows, indicating that the source use case is dependent on the target use case.

"Arrow pointing": pointing to a dependent

5. Project (Artifact)

Use case diagrams are used to help people visualize functional needs, but few people can understand it. Many times communicating with users or even using Excel is stronger than use case diagrams, and VS2010 introduces an element such as "project," which allows developers to link a common document in a use case diagram.

To rely on a use case on a project:

Then set the hyperlink of the project-"attribute" to your document;

This opens the associated document when you double-click the item on the use case diagram.

6. Notes (Comment)

includes (include) , extension (extend) , generalization (inheritance) The difference:

Conditionality: The sub-use cases in generalization and included in the include are unconditionally occurring, while the occurrence of extension cases in extend is conditional;

Directness: Child use cases in generalization and extension cases in extend provide direct service to participants, while the use cases included in the include provide indirect services to participants.

For extend, the extension use case does not contain the content of the underlying use case, nor does the underlying use case contain the content of the extension use case.

For inheritance, a child use case contains all the contents of the underlying use case and its relationship to other use cases or actors;

A use case diagram example:

Complaints:

The sense of use case diagram is not mature enough to express the requirements of the system, and users without a uml background are hardly aware of what is being painted.

Secondly, the arrow symbols that contain the relationship and extend the relationship are the same arrows, which can be distinguished only by writing a text above, and translated into other languages, almost without knowing what it means. The arrow facing the extended relationship is also difficult to understand, why point to the base use case, not to the extension use case.

VS2010 adds a "project" element, which is a great innovation to associate Word, Excel, in a use case diagram. But why not integrate these functions directly into the use case, double-click the use case to pop up a document is not much easier to understand, it is necessary to add a component, just to provide a link function.

Use Case Description Table:

Since the use of diagram does not clearly express the functional requirements, the development of people usually use a description table to supplement some difficult to express use cases, the table provides a reference for you:

Original: http://kb.cnblogs.com/page/129491/

UML Modeling use case diagrams