First, UML's documentation, the definition of use case is: Definition and description of a consistent functional unit of a system or subsystem without presenting a system or subsystem. Use Cases itself is an interaction with a user or other system with a designed system. Here I think two words that we must focus on "Features" and "Interaction".
Second, how to write USE CASE? (1) When writing USE CASE, you must imagine yourself to enter this system, interact with the system, and USE CASE will mention the UI, unless this UI is related to the function. (2) Seize the Actor of the system, which Actor, which features provide any of the system. Actor is independent of the system; actor is the function provided using the system. (3) Use case itself is highly polymerized, and the USE case should be low coupling, which means that it is necessary to describe this USE CASE when describing a USE CASE. Do not involve other USE CASE. It is important to maintain a small particle size of each use, and the function is single, and do not involve it in this case. (4) Pay attention to the description of Use Case itself, the relationship between USE CASE does not have to pay too much attention. Don't put the focus on the relationship between the use case (in the end, it is still extended, generally), there is no great value for your use case or for your system. (5) How to describe a step of using USE CASE? To grasp "degree": For example, there are three descriptions. A. User Enter information b. User Enter the username and password c. User enters the username and password in the edit box. It is obvious that B is the most appropriate. (6) Use case to explicitly start and end
Third, the problem of crud operation is a branch path in a USE CASE, or as a separate usecase, my opinion is that this Crud logic is more complicated, if the logic is simple, put it in one Uses will be better and compact. Fourth, the expansion event flow is used to describe some abnormalities and select branches. When there is conditional judgment, the system is used to test ... do not use words "if". At the same time, a conditional branch is selected as the primary path of the USE CASE, and other conditional branches are placed in the extended event stream.
