What is a three-tier structure?

The presentation layer is like a waiter in a restaurant, the business logic layer is like a chef in a restaurant, and the data access layer is like a buyer in a restaurant. You are a customer. If you want to eat in a restaurant, you should order from the waiter first. The waiter will tell the chef what you ordered. The buyer will buy the materials that the chef needs for cooking. The buyer will buy them back for the chef. The chef will ask the waiter to deliver the food to you.

Presentation layer

The interface that the presentation layer displays to the customer service.

Business logic layer

Business logic layer handles business (non-null judgment, etc.). ).

Data access layer

The data access layer accesses the database.