Why is it important to limit dependencies between layers?

Limiting dependencies between layers matters because it is exactly what makes a system resilient, understandable, and manageable. If the layers get "tangled" together, the architecture quickly turns into chaos.

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#1. To avoid "spaghetti code"

When every layer can reach any other layer, logic gets mixed together: the interface reaches directly into the database, business rules are scattered across the UI and SQL queries. Making changes becomes scary: one change breaks everything else.

Conclusion: limiting dependencies keeps the system in order and makes it predictable.

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#2. To be able to change technologies

If the UI only knows the business logic, not the database, it becomes possible to:

• replace SQL with NoSQL,
• rewrite the interface from React to Flutter,
• extract the API into a microservice. And all of this without rewriting the rest of the code.

Conclusion: loose coupling = flexibility and room to grow.

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#3. To make testing simpler

When each layer is isolated, the business logic can be tested without the interface and the database, by plugging in stubs (mocks). This sharply reduces the cost and complexity of testing.

Conclusion: independent layers = easy test coverage.

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#4. To keep the system understandable and scalable

With strict dependencies, it is clear where the logic is, where the data is, and where the interface is. New developers get oriented quickly, and scaling does not turn into a disaster.

Conclusion: limiting dependencies is not bureaucracy, it is a way to keep control over the project's growth.

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Summary:

The weaker the connections between layers, the stronger the architecture. It is like a healthy spine: each vertebra holds its own level, which is why the whole body can move freely.