Hexagonal architecture (software): Difference between revisions

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The '''hexagonal architecture''', or '''ports and adapters architecture''', is an architectural pattern used in [[software design]]. It aims at creating loosely coupled application components that can be easily connected to their software environment by means of ports and adapters. This makes components exchangeable at any level and facilitates test automation.<ref name=":0">{{Cite web|url=http://alistair.cockburn.us/Hexagonal+architecture|title=Hexagonal architecture|last=Alistair|first=Cockburn|date=2005-04-01|website=alistair.cockburn.us|archive-url=https://web.archive.org/web/20180822100852/alistair.cockburn.us/Hexagonal+architecture|archive-date=2018-08-22|dead-url=yes|access-datestatus=dead}}</ref>

== Origin ==

The hexagonal architecture was invented by [[Alistair Cockburn]] in an attempt to avoid known structural pitfalls in [[Object-oriented analysis and design|object oriented software design]], such as undesired dependencies between [[Layer (object-oriented design)|layers]] and contamination of [[user interface]] code with [[business logic]], and published in 2005.<ref>{{Cite web|url=https://www.infoq.com/news/2014/10/exploring-hexagonal-architecture/|title=Exploring the Hexagonal Architecture|last=Stenberg|first=Jan|date=2014-10-31|website=InfoQ|archive-url=|archive-date=|dead-url=|access-date=2019-08-12}}</ref>

The term "hexagonal" comes from the graphical conventions that shows the application component like a [[hexagon]]al cell. The purpose was not to suggest that there would be six borders/ports, but to leave enough space to represent the different interfaces needed between the component and the external world.<ref name=":0" />

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== Variants ==

The onion architecture proposed by Jeffrey Palermo in 2008 is similar to the hexagonal architecture: it also externalizes the infrastructure with proper interfaces to ensure loose coupling between the application and the database.<ref>{{Cite web|url=https://jeffreypalermo.com/2008/07/the-onion-architecture-part-1/|title=The Onion Architecture : part 1|last=Jeffrey|first=Palermo|date=2008-07-29|website=Programming with Palermo|language=en-US|archive-url=|archive-date=|dead-url=|access-date=2019-08-12}}</ref> It decomposes further the application core into several concentric rings using [[inversion of control]].<ref>{{Cite book|url=https://www.worldcat.org/oclc/937787252|title=Learning NHibernate 4 : explore the full potential of NHibernate to build robust data access code|last=Chatekar, Suhas,|first=|publisher=Packt Publishing|year=2015|isbn=978-1-78439-206-2|___location=|pages=249–250|oclc=937787252}}</ref>

The clean architecture proposed by [[Robert C. Martin]] in 2012 combines the principles of the hexagonal architecture, the onion architecture and several other variants; It provides additional levels of detail of the component, which are presented as concentric rings. It isolates adapters and interfaces (user interface, databases, external systems, devices) in the outer rings of the architecture and leaves the inner rings for [[use case]]s and [[Entity class|entities]]<ref>{{Cite web|url=https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html|title=The Clean architecture {{!}} Clean Coder Blog|last=Martin|first=Robert, C.|date=2012-08-12|website=blog.cleancoder.com|archive-url=|archive-date=|dead-url=|access-date=2019-08-12}}</ref>^,.<ref>{{Cite book|url=https://www.worldcat.org/oclc/1004983973|title=Clean architecture : a craftsman's guide to software structure and design|last=Martin, Robert C.,|first=|publisher=Prentice Hall|year=2017|isbn=978-0-13-449416-6|___location=|pages=|oclc=1004983973}}</ref> The clean architecture uses the principle of [[Dependency inversion principle|dependency inversion]] with the strict rule that dependencies shall only exist between an outer ring to an inner ring and never the contrary.

== See also ==