The architecture of something screams the intent.

—Robert C. Martin

Often when looking at the code of web applications, you are greeted with a mass of folders, library installation, and tooling configurations. The code is structured haphazardly into nondescriptive folders like app, and the dependency layout of the application is a jungle.

As a result, the purpose and architecture of the program become opaque.

The architecture of an application is driven by its use cases.

—Ivar Jacobsen

The idea is to design programs so that their architectures immediately present their use case. It’s a way to design programs so that its internal dependency graph is organized cleanly and its elements are joined together with as loose coupling as possible.

Ultimately, the goal is the separation of concerns between application layers, this architecture and many like it aren’t dependent on presentation models or platforms. All the arrows, or dependencies, point inwards in the abstraction chain, each successive layer less abstract than the one before it.

Keeping the arrows pointing inwards makes the code easy to maintain, extend, test and refactor. EBI imposes some architectural requirements on the programmers, that is, you must navigate around its rules, but this is kept at a minimum.

How does this archtecture differ from MVC?

The difference between EBI and MVC is that an EBI architecture is that the business logic of the application is designed to be platform-agnostic of its delivery mechanism.

To paraphrase, this means that the business logic parts, interactors and entities, do not know in which medium they’re being accessed from. It could be from a web server, a unit test, or a GUI application.

Contrast this to MVC, where there is always a dependency on the delivery mechanism. No matter how hard you tried, you cannot tear Rails controllers out of the web world.

What makes decoupling the business logic from the delivery mechanism a good thing? This is outlined in the next section, `ref`:design:.