Explain what is Dependency Rule in Clean Architecture

The Dependency Rule is a fundamental principle in Clean Architecture that dictates how dependencies between different layers of a software system should be managed. According to this rule, source code dependencies must always point inward, towards higher-level policies and domain logic, and never outward towards lower-level implementation details. This means that the inner layers of the system, which contain the core business logic and high-level policies, should not depend on the outer layers, which include technical details like the user interface, database, and external frameworks[1][3][4][5][6].

Key Aspects of the Dependency Rule:

1. Inward Pointing Dependencies:

   • Dependencies should always point towards the more abstract, stable parts of the system. The inner layers should be independent of the outer layers, ensuring that changes in the outer layers do not affect the core business logic[1][4][5].

2. Separation of Concerns:

   • By adhering to the Dependency Rule, Clean Architecture achieves a clear separation of concerns. The business rules and domain logic are isolated from technical details, making the system more modular and easier to maintain[1][4][5].

3. Use of Interfaces:

   • To enforce the Dependency Rule, interfaces or abstract classes are often used. These abstractions allow the inner layers to define what they need from the outer layers without depending on their concrete implementations. This way, the outer layers can implement these interfaces, ensuring that the core logic remains unaffected by changes in the outer layers[1][3][4][6].

4. Flexibility and Testability:

   • Following the Dependency Rule makes the system more flexible and testable. Since the core logic does not depend on external frameworks or tools, it can be tested independently. This also allows for easier swapping of components, such as replacing a database or user interface, without impacting the core business logic[1][3][4][5].

Practical Example:

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