What does the "dependency rule" mean?

The Dependency Rule is the core principle of Clean Architecture that defines the direction of dependencies between the system's layers.

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#The essence of the rule

All dependencies point inward, toward the center of the architecture.

Inner layers (business logic) must know nothing about outer ones (infrastructure, UI, frameworks).

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#What it looks like

• Code in an outer layer can call into an inner one.
• An inner layer must not depend on an outer one, only on abstractions (interfaces) defined within itself.

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#Example

• Allowed: a controller calls CreateOrderUseCase.
• Not allowed: CreateOrderUseCase uses Django ORM or Flask directly.

Instead, the use case calls the OrderRepository abstraction, and an adapter (an outer layer) implements that interface using a specific technology.

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#Why it matters

1. Isolate business logic from frameworks.
2. Make the system independent of external changes.
3. Make testing and technology replacement easier.

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Summary:

The Dependency Rule states that dependencies always point from details to abstractions, and from outer to inner, so the system's core stays stable, clean, and independent.