What are the three layers of the three-tier architecture?

Three-tier architecture (3-tier architecture) In the usual sense, the three-tier architecture divides the entire business application into: User Interface layer (User Interface layer), Business Logic Layer (Business Logic Layer), and Data Access Layer (Data access layer).

#The purpose of distinguishing levels is the idea of ​​"high cohesion and low coupling". In software architecture design, the hierarchical structure is the most common and important structure.

The layered structure recommended by Microsoft is generally divided into three layers, from bottom to top: data access layer, business logic layer (also known as domain layer), and presentation layer.

As the name suggests, the three-tier architecture is divided into three layers, namely "data access layer", "business logic layer" and "presentation layer". (Recommended learning: PHP video tutorial)

The three-tier architecture software system creates convenient conditions for users’ data transmission, extraction, and storage. When applying data, the information division architecture development project clearly plans the work responsibilities between each level, thus reducing the maintenance risk of the website system.

Presentation layer

The presentation layer is also called the presentation layer UI. It is located at the top of the three-tier architecture and is in direct contact with users, mainly in the B/S information system. Wed browse the page. As a Wed browsing page, the main function of the presentation layer is to realize the incoming and outgoing of system data. In this process, the data can be transmitted to the BBL system for data processing without relying on logical judgment operations. After processing, the processing results will be fed back. into the presentation layer. In other words, the presentation layer implements user interface functions, communicates and feedbacks user needs, and uses BLL or Models for debugging to ensure user experience.

Business logic layer

The function of the business logic layer BLL is to make logical judgments and execution operations on specific problems. After receiving user instructions from the presentation layer UI, it will connect Data access layer DAL, the access layer is located in the middle of the presentation layer and the data layer in the three-layer architecture. It is also the bridge between the presentation layer and the data layer. It realizes the data connection and instruction transmission between the three layers, and can perform logical processing on the received data. , realize data modification, acquisition, deletion and other functions, and feed the processing results back to the presentation layer UI to realize software functions.

Data Access Layer

Data access layer DAL is the main control system of the database, which implements operations such as adding, deleting, modifying, and querying data, and feeds back the operation results. To the business logic layer BBL. In the actual operation process, the data access layer has no logical judgment ability. In order to achieve the rigor of code writing and improve the code reading level, generally software developers will write DataAccessCommon in this layer to ensure the DAL data processing function of the data access layer.

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