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

---

### 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).

---

### What it looks like

```javascript
[ Frameworks & UI ]
        ↓
[ Interface Adapters ]
        ↓
[ Use Cases ]
        ↓
[ Entities ]
```

- 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.

---

### Why it matters

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

---

**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.

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