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Introducing IODA Architecture

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For Ralf Westphal common architectural patterns like Layered architecture, Hexagonal architecture and Clean architecture all look very similar doing the same two things: defining domains of responsibility and putting functional dependencies in order. For him these patterns give a very crude idea of the structure of an application, essentially describing software as a deep hierarchy of functional or behavioural dependencies.

Looking for another way of describing architecture Westphal has defined an architectural style, IODA Architecture, built on three formal responsibilities, orthogonal to behavioural responsibilities:

IODA Architecture Operation is a piece of logic or behaviour working on some data but not aware of any other operation and not allowed to call them.
Data is a structure of data possibly including services working on the data to ensure consistency but not containing any other form of logic.
Integration calls operations and other integrations to put everything together thus creating behaviour but they do not contain logic.
APIs and frameworks is a fourth part through which operations interact with the environment.

In this model operations depends only on data and integrations depends on operations and other integrations. By this Westphal claims to have removed all functional dependencies, what remains are just what he calls formal or empty dependencies. He also claims that since operations cannot call other operations, extracting logic into new operational methods implies creating integrations to keep things together thus enforcing small methods, less than 10-20 lines of code, within an application.

An important aspect Westphal mentions is that a IODA structure can appear at several levels. What is an operation at one level of abstraction can itself be a complete IODA structure when zooming in.

Westphal has created an example of how to design and implement a small application using IODA including a description of the basic ideas behind the design and with the code available for download.

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