Why separate layers

Splitting the app to layers help maintain, decouple, and scale.

What is it

Most popular implementation of multi-tier architecture:

Handles the user interface and user interactions, presenting information to users and capturing user input

Intermediate between Presentation and Data Access layers.

This layer handles business logic, business rule, and calculations.

Defines how data from the database can be retrieved and used, what it can perform, and cannot perform.
Repsonsible for processing and manipulating data before it is presented to the user or stored in the database.
Run validation to ensure that data meets business rules and constraints.
Enforce business rules and policies like access control, authorization, and authentication.

Stores, maintains, and manages data structurally and organizationally

Interacts with the user and the business layer

Store/retrieve Data Performs further processing Pass result to the presentation layer Respond to user requests