Layered architecture is a way to organize an application by dividing it into separate, logical layers. Each layer has a specific responsibility and communicates only with the layers directly above or below it. The most common layers include:

• Presentation layer: handles user interface and user interactions;
• Business logic layer: processes data, applies business rules, and makes decisions;
• Data access layer: manages communication with databases or external storage.

This structure helps you maintain a clean separation of concerns. By keeping each part of the application focused on a single responsibility, you make the system easier to develop, test, and update. Changes in one layer, such as updating the database technology, will have minimal impact on the others. This approach leads to more maintainable and scalable applications.

Benefits of Layered Architecture

Layered architecture offers several key advantages that make it a popular choice for building complex systems:

• Maintainability: Each layer is responsible for a specific aspect of the system, making it easier to locate, update, or fix code without affecting unrelated parts;
• Testability: You can test each layer independently, allowing you to identify and resolve issues more efficiently;
• Clear boundaries: Layers define strict boundaries between system components, reducing the risk of unintended interactions and making the overall design easier to understand and document;
• Reusability: Common functionality can be grouped into a single layer and reused across different modules or applications.

Common Limitations

Despite its benefits, layered architecture also introduces some challenges:

• Rigid structure: Strict separation between layers can lead to inflexibility, making it difficult to adapt to new requirements or integrate new technologies;
• Slower changes between layers: Modifications that require coordination across multiple layers can be time-consuming and may slow down development;
• Potential performance overhead: Data and requests must pass through each layer, which can add unnecessary processing and reduce system efficiency if not managed carefully.

Typical Layers in Layered Architecture

Here is a simple ASCII diagram that shows the three main layers you typically find in a layered architecture:

+----------------------+
|  Presentation Layer  |
+----------------------+
|   Business Logic     |
|       Layer          |
+----------------------+
|   Data Access Layer  |
+----------------------+

• Presentation Layer: handles user interface and user interaction;
• Business Logic Layer: processes data, enforces rules, and coordinates application activities;
• Data Access Layer: communicates with the database or other storage systems.

Practical Example: When to Use Layered Architecture

Suppose you are building an online bookstore. You want to keep your code organized so that changes in one area do not affect others. Layered architecture is an excellent fit for this scenario because it separates the application into distinct layers, each with a clear responsibility:

• Presentation layer: Handles user interactions, such as browsing books or placing orders;
• Business logic layer: Processes actions like validating payments or calculating shipping costs;
• Data access layer: Manages all communication with the database, such as retrieving book information or storing order details.

If you need to update the user interface or change the database system, you can do so without rewriting the entire application. This separation makes the system easier to maintain, test, and scale as your bookstore grows.