Layered Architecture (N-tier)

Simplest form of software architecture, dividing software into horizontal layers.

Common Layers:

• Presentation Layer (User interfaces)
• Business Logic Layer (Application logic)
• Data Access Layer (Database interactions)

Structure:

graph TD
    P[Presentation] --> B[Business Logic]
    B --> D[Data Access]
    D --> DB[(Database)]

Example:

An online store can use a layered structure:

• Presentation Layer: Product pages, cart screen, and checkout form.
• Business Logic Layer: Pricing rules, discount validation, stock checks, and order processing.
• Data Access Layer: Queries for products, customers, inventory, and orders.

When a customer places an order, the UI sends the request to the business layer, which validates the order and then uses the data layer to save it.

Pros:

• Easy to understand, widespread usage.
• Simple separation of concerns.

Cons:

• Tends toward tight coupling.
• Harder to change foundational layers later.

When to use:

• Simple CRUD applications.
• Small to medium-sized web apps.

Check Your Understanding

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What is the defining rule of a Layered Architecture?

Each layer depends only on the layer below it, and each layer has one responsibility

Correct. The strict form forbids skipping layers, which keeps the structure predictable, at the cost of extra pass-through code.

Every layer may call every other layer freely

Layers communicate only through asynchronous events

Each layer is deployed as an independent service

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