Use Case Diagram(用例图)

Capturing the dynamic behavior of a system.(dynamic behavior refers to the behavior of the system when it is running/operating.
use case diagram is dynamic in nature, the internal and external factors for making interaction

Use Case Diagram consists of actor, use cases and their relationship

A single use case diagram captures a particular functionality(特定功能) of a system!

Purpose of Use Case Diagrams

Use Case Diagrams are to capture the dynamic aspect of a system. ====》 the definition is too generic to describe the purpose.

Use Case Diagrams are to gather the requirements of a system

When a system is to gather its functionalities, use cases are prepared and actors are identified.

🥗 In bried, the purpose of use case diagrams can be said to be as follows
🔺 gather the requirements of a system
🔺 get an outside view of a system
🔺 identify the external and internal factors influencing the system
🔺 show the interaction among the requirements are actors

How to draw a Use Case Diagram?

use cases are nothing but the system functionalities written in an organized manner.
actors can be a human user, some internal applications or may be some external applications.

🎄 Planning to draw a use case diagram, we should have the following items identified.
🔹 Functionalities to be represented as use case
🔹 Actors
🔹 Relationships among the use cases and actors.

Use case diagrams are drawn to capture the functional requirements(功能需求） of a system.

The guidelines for drawing a use case diagram

🥖 the use case's name can identify the functionalities performed.
🥖 a suitable name for actors.
🥖 show relationships and dependencies clearly in the diagram.
🥖 only provide the main purpose of the diagram is to identify the requirements.
🥖 use notes whenever required to clarify some important points.

Where to Use a Use Case Diagram?

five diagrams(use case、sequence、collaboration、statechart、activity) in UML is to capture the dynamic behavior of a system.
each and every model has some specific purpose to use. In fact, analysis a running system from different perspectives.

🏳‍🌈
Use case diagrams specify the events of a system and their flows.
But use case diagram never describes how they are implemented.
Use case diagram can be imagined as a black box where only the input, output, and the function of the black box is known.

In forward engineering, use case diagrams are used to make test cases and in reverse engineering use cases are used to prepare the requirement details from the existing application.

Use case diagrams can be used for

  - Requirement analysis and high level design.
  - Model the context of a system.
  - Reverse engineering.
  - Forward engineering.

用例图方面优秀博文：
1. https://www.cnblogs.com/gd-luojialin/p/10356704.html
2. https://kb.cnblogs.com/page/129491/
3. https://www.cnblogs.com/lcword/p/10472040.html
4. https://baike.baidu.com/item/用例图/9531932?fr=aladdin