Unified Modeling Language (UML) use case diagram

Unified Modeling Language (UML) use case diagramThe use case diagram describes a functional unit provided by the system. The purpose of the use case diagram is to help the development team understand the functional requirements of the system in a visual manner, including the relationship between "Roles" based on the basic process, and the relationship between use cases in the system. The use case diagram is generally used to represent the Organizational Relationship of use cases. It is either a set of Use Cases of the entire system or a set of Use Cases with functions (for example, all security management-related use cases. Use Case refers to the system function, which is a collection of all the execution actions of a system function. Use Cases are described from a user's point of view. This user tells the system to do something specific. A Use Case captures the visual sequence of an event, which is a response process in which a system inspires a single user (stimulus. An actor represents a role that a system user can assume ). These users may be people, other computers, some hardware, or even other software systems. The only requirement for use cases is that they must be located outside the system section of the use case description. They must be able to stimulate the System Section and receive responses. Use Cases describe the system activities when an animation author gives a specific stimulus to the system. These activities are described in text. It describes the essence of the stimulus that triggers the use case, the input and output to other activists, and the activities from input to output. The use case text usually also describes the possible errors of each activity and the remedial measures that the system should take. In the use case diagram, an elliptic is used to represent the use case, and the name of the use case is placed in the center of the elliptic or in the center of the elliptic. A humanoid symbol is used to represent a role (user ). The relationship between the role and the use case is described by a simple line segment, indicating that the role can operate on the use case. In the use case diagram, a box is used to represent the boundaries of the system. All system use cases are placed in the box, and all animations are located outside the box. The author and the use case are connected in a straight line. Everything in the box is part of the system, and everything outside the box is external to the system. The use case diagram contains six elements: Executor, use case, association, include, and extended relationship) and generalization ).
1. performer)

2. Use Case)

3. Relationship between Use Cases
3.1 Association)
An association is used to connect an actor and use case, indicating that the actor executes the use case function.

3.2. Include)
The inclusion relationship comes from the abstract of use case, that is, the common parts are separated from several different use cases to become reusable use cases.

3.3. Extended relationship (extend)
The extended relationship indicates that another use case may be inserted temporarily according to the condition in the conversation process of a use case. The former is called the basic case, and the latter is called the extension case.

3.4. Generalization)
It is similar to the parent class and subclass in Java.
Figure 6-2 shows an example. The use case diagram is usually used to express advanced functions of the system or system category. In the figure, you can easily see the functions provided by the system. This system allows the band manager to view the sales statistics and ranking reports of the band CD. It also allows the recording manager to view the sales statistics reports of specific CD and the reports of these cd in the ranking. This figure also tells us that the system will provide the ranking report through an external system named "ranking report service. The use case diagram does not list functions that cannot be completed by the system. The system shown in cannot provide the band manager with a method to listen to the songs in different albums on the ranking. That is to say, the system does not reference a use case called "listen to the songs on the ranking. If clear and brief use case descriptions are provided in the use case diagram, the project sponsor can easily see whether the system provides the required functions.