What is the "presentation layer"?

The presentation layer (or level of representation, presentation layer) is the top level of layered architecture, responsible for the system's interaction with the user.

Its task is to display data in a convenient form and capture input from the user.

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#Main functions of the presentation layer:

1. Displaying information - visualizes data received from the business logic (for example, shows a list of products, a user profile, search results).
2. Handling input - accepts the user's actions (clicks, text input, choosing options) and passes them further, to the logic layer.
3. Validation - can perform primary data checks (for example, that a field is not empty, that an email's format is correct, and so on).
4. Connection to the application logic - does not process business rules, only calls the needed methods of the lower layers (usually through controllers, an API, or services).

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#Presentation layer examples:

• In a web application - the HTML/CSS/JS interface, React or Vue components, MVC controllers.
• In a mobile application - screens, UI elements, the View-Model in MVVM.
• In a desktop program - windows, buttons, forms, data tables.

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#The key idea:

The presentation layer should not "know" how the business logic or the database is built. It only displays the result and passes the user's actions further on