多层框架结构是几层

H2标签不能用中文或者其他语言替代，因此以下的H2标签为英文，虽然可能会导致阅读困难。

Introduction

Web development has come a long way since the inception of the internet. Today, web developers have a vast range of tools at their disposal, with which they can create complex and dynamic web applications. In the process of designing these applications, web developers often use different techniques to structure their code, one of which is the concept of multi-layered framework structures.

Body

Multi-layered framework structures are used to help organize and define the roles of the different components of a system. The structure is designed to separate the different layers, allowing developers to work separately on each layer while still maintaining a cohesive and efficient application. These structures are typically made up of three or more layers, each with a specific function.

The first layer is the presentation layer, also known as the user interface layer. This layer is responsible for rendering the user interface elements that the user interacts with, such as web pages or mobile apps. The presentation layer can be designed using HTML, CSS, and JavaScript.

The second layer is the business logic layer, also known as the control layer. This layer is responsible for handling the application's logic, processes, and workflows. The business logic layer uses programming languages such as PHP, Node.js, and Python to implement the application's functionality.

The third layer is the data access layer, also known as the persistence layer. This layer is responsible for interacting with data storage systems such as databases, file systems, and other data sources. The data access layer can be designed using SQL, MongoDB, and other database management systems.

Some frameworks may have additional layers, but the essential three layers mentioned above are the most common. The purpose of these layers is to provide a separation of concerns, so that each layer can be developed, tested, and maintained independently.

Conclusion

Multi-layered framework structures are essential in the development of complex web applications. They help to increase the efficiency of the application by providing a clear separation of concerns among the different layers. The presentation, business logic, and data access layers each have a specific function and can be developed, tested, and maintained independently. By using frameworks that implement these structures, developers can create high-performance applications that are easy to maintain and update.