Why is the use case not a "function "? Yes? Or not? [Original]

I read an article todayArticleThis is a misunderstanding of use cases. I have a big feeling, and I don't have the same opinion as my boss. So I want to confirm whether or not I agree with my boss?
I believe everyone has read this article "why is the use case not a" function "?"
I would like to elaborate on some of my own points below. If anything is wrong, you are welcome to correct them.
1. Use cases should be conducted after requirement research and before requirement analysis.
2. Use Cases should run through the early stage of the project (requirements and design ).

What do we first think when we receive a project task? What does the customer want to do through this software?
In this case, you can obtain general requirements through demand research.
What we need to do now is use cases (can be called Concept-level use cases)
What is "concept-level use cases" is to describe the special cases of software to express what the software is about to accomplish, and describe how something is useful to them using the system, it describes what the system does at the conceptual level, so that we can understand the system enough to determine whether the system needs to do the right thing. Concept-level use cases form a conceptual model of a system ..

Example 1.

What do customers want to do with the software?

After completing the system-level use cases and clarifying what the customer needs to do with the software, we will synchronize the demand analysis and summarize the requirements according to the use cases. This is an iterative process.
When our requirements are analyzed in detail, the design is also at this stage. The next layer of the use case diagram is the function-level use case.
Function-level use cases are used to describe specific functional details.CodePreparation. This is the "Use Case" that many of us usually understand ",
Examples in the minds of many people (including my previous ones:
Example 2

Description function-level relationship
Focus on Value

Many people think that use cases cannot be used first. I think use cases can drive requirement analysis or design iteration.
The first use case is a concept-level use case used to describe the coarse-grained service of the software, so as to clarify the true purpose of the software, so as to suppress the distortion and uncontrollable demand of the software. (Of course, demand management plays a crucial role)
After the outline design is complete, the demand analysis enters the detailed analysis stage, and the use cases are refined to implement function-level use cases. For detailed design.

Example

Consider an e-commerce system that you have used on the Internet. When you log on to this site, your goal may be to search for product-related information, select the product to be purchased, arrange payment, and deliver the goods. In the process of doing this, you may change your mind, enter the wrong information, and have to modify it, change the mail or delivery address, and other things. If this website does not allow you to find and order products in an attractive way, you may not complete your order, let alone come to this website again.

When building a system, always remember the core definition of the use case: a story about using the system in a certain way to do valuable things. If you can implement this definition to show the values that users want to obtain through the system, and then create use cases that reflect these values, your system will better meet user expectations.