Software Architecture: 3-Layer Model / 3-Tier

This article is a term explanation for the 3-layer model (3-tier) – including exam questions, key points and tags.

In a Nutshell

The 3-layer model logically separates software into presentation, business logic and data access – for clear responsibilities, maintainability and testability.

Compact Technical Description

The three layers:

1. Presentation (UI)
2. Business Logic (Services/Use Cases)
3. Persistence (Repository/ORM/DB)

Communication typically occurs from top to bottom. Each layer only knows the one directly below it. This makes systems loosely coupled.

Exam-Relevant Key Points

• Separation of presentation, logic, data access
• Clear responsibilities
• Better testability/maintainability
• Standard in Java/.NET/web projects (IHK-relevant)
• Components are interchangeable (UI changes)
• Layers are security barriers
• Modularization reduces follow-up costs
• Architecture must be documented

Core Components

1. Presentation layer
2. Logic layer
3. Data access layer
4. Interfaces between layers
5. Logging/error handling
6. Unit tests in business layer
7. DTOs
8. Security layer
9. Persistence (SQL/NoSQL)

Practical Example

UI (HTML/JS): Input
Business (Controller/Service): Validation/Processing
Persistence (ORM/MySQL): Storage

Advantages and Disadvantages

Advantages

• Structured, maintainable application
• Easy component replacement
• Good testability

Disadvantages

• Initial higher effort
• Overhead in very small projects

Typical Exam Questions (with Short Answers)

1. What does the 3-layer model describe? Presentation, logic, data access.
2. Which layer validates input? Business logic.
3. What belongs to the data access layer? DB access, SQL/ORM, repositories.

Free Answer

For IHK projects, the model is ideal because it is easy to draw and justify. Important: no SQL in the controller and no database access from the UI.

Learning Strategy

1. Draw the model for a system (shop/blog).
2. Implement CRUD app strictly according to layers.
3. Explain layers in project documentation.
4. Implement separation technically through packages/namespaces.

Further Information

1. https://c4model.com/