Ports and Adapters

In Growing Object-Oriented Software, Guided By Tests its authors explain how they grow systems a slice of functionality at a time. As the code scales up, they need to structure the functionality so they can continue to understand and maintain it. They use two principal heuristics to guide this structuring:

1. Separation of concerns.
2. Higher level of abstraction.

They state that, when applied consistently, these two forces push the structure to something similar to Cockburn's "ports and adapters" architecture.

These are the links I'm reading to find out what this "ports and adapters" (or hexagonal) architecture is about:

• Original description by Alistair Cockburn
• Ports and Adapters architeture (C2 wiki)
• Hexagonal Architecture (C2 Wiki)
• Ports and Adapters in Garfixia Software Architectures Dossier
• A kata using it by Matteo Vaccari