The business logic of an application is a description of the schemes by which the application interacts with the user. When a user subscribes, or fills out an order form, or simply logs in, all these actions are processed “under the hood” of the application in a specific order.
What data do you need to request? Does the entered data match the specified format? What happens after the user clicks the "Confirm" button? Does he even have access rights to this operation? All these and many other questions can be answered by examining how the business logic of a particular application is built.
The simplest example: an airline administrator (user) registers a passenger for a flight (enters information into the database).
What the user does:
1. Opens information about the selected flight, goes to the list of already registered passengers, clicks "Register passenger".
2. Fills in the registration form: enters the flight number, selects a passenger, indicates the place and status of check-in.
3. Presses the "Confirm" button
4. Sees a new passenger in the general list.
How it looks from the point of view of the application's business logic:
1. The application checks if the user is authorized and has access rights to the selected page, as well as registration operations.
2. Waits for the user to fill out the form.
3. Processes the entered data:
a. Checks if the entered data meets the requirements of the application (these requirements are predefined by the programmer): for example, the field "Flight number" must contain an integer.
b. Receives information from the database: for example, about a flight and related registrations (to make changes), a passenger (to check if this passenger is actually in the database).
c. Shows error messages if the fields are filled incorrectly.
d. Sends information to the database, giving commands to create new records in it or update existing ones.
4. Displays updated information on the screen.
The general logic of the application is being built by business processes - diagrams describing specific operations in the system: creating a passenger record, adding to the system new flight, editing registration information.
When it comes to classical programming, blocks of code are used to describe all processes. Many of them are written according to templates - they are simply used in a different sequence and to work with different data.
Because of this "template" nature in no-code development, it became possible to use visual programming tools - business logic designers. They help to select the necessary blocks, set up and arrange them in the desired sequence and even create some blocks automatically, depending on the settings of other components of the application. The bottom line is ready-made business logic without having to spend hours and hours over lines of code.