Architectural layer

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The architectural layer generally encapsulates a software application's technical complexities independent of the business logic, thereby providing a loose coupling between the business functionality and the underlying technical infrastructure.

Layered architectures contribute to the high availability of software infrastructures by enabling components to detect failure of components in adjacent layers: this in turns insulates architectural components and protects them from failures in other layers.

One of the key properties of a layered architecture is that the higher layer has knowledge of the lower layer, while the lower layer must not make any assumptions on the higher layers. In a multli-layered architecture, it is valid for a layer to skip lower other layers but it still must not have dependencies on higher layers.

There is often a confusion between layers and tiers. Layers are defining a logical structure of the code. They do not tell anything about the physical deployment. Tiers, on the other hand, are talking about the physical structure and how the application can be deployed. In other terms, layers are running in tiers.

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