Layered system

Most modern applications are designed using multiple layers, and the same is expected from a RESTful service. In a layered system, each layer is restricted to only seeing or knowing the next layer in the hierarchy.

Having a layered architecture helps improve the code's readability, hides complexities, and improves the code's maintainability. Imagine that you have one layer and everything takes place in it, from authentication to database operations. This is absolutely not recommended, as the primary components, such as authentications, business logic, and database operations, are not separated out.

Thus, this constraint is expected from a RESTful service, and no client can actually say that it is connected to the final layer.