The Four Architectures That Will Inspire Your Programming
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This is the Big 4. The architectures, that may help your work. They may influence the way you think about programming.
1. The Hexagonal Architecture
(also known as the Ports and Adapters)
Originally described by Alistair Cockburn in http://alistair.cockburn.us/Hexagonal+architecture.
Enhanced and popularised by Steve Freeman and Nat Pryce, thanks to their book: http://www.growing-object-oriented-software.com/
2. Clean Architecture
Originally described by Ivar Jacobson, but popularised by Uncle Bob: http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html
DDD: Domain-Driven Design
CQRS: Command Query Responsibility Segregation
Two separate concepts, but together create quite a unique architecture.
DDD is originally invented by Eric Evans. CQRS is often popularised by the work of Greg Young.
DCI: Data Context Interaction
James Coplien, Trygve Reenskaug
Desribed in James' book: http://www.leansoftwarearchitecture.com/ and here: http://www.artima.com/articles/dci_vision.html
What I think about them
I don't treat them as competitors. Learning the concepts behind them (still in progress) inspired me to bring some new ideas to our projects. Usually, they're not all or nothing.
The most mind-blowing architecture is definitely DCI. This is the future of programming. The vision of objects being different things in different contexts, while still keeping its identity is fantastic. Unfortunately, DCI is also the hardest one to use in day-to-day practice. Some of the concepts required (objects with roles) are hard to achieve in most popular languages.
The most practical architecture is possibly DDD/CQRS. There is a lot of example projects in many different languages. I love the pragmatic approach of splitting the system into Commands and Queries. At first, I couldn't get the point, but after more reading I see the beauty of it. I sometimes laugh that DDD could stand for (data) Duplication-Driven Design. It opened my eyes to the idea, that we can have multiple subsystems, each with its own storage. Some data will be duplicated this way, but it's often not a problem. The data is eventually consistent.
Another nice thing about DDD is the idea of Bounded Contexts. It's a terrible name, but a really useful concept of a module that encapsulates one little world of your project. Usually, you have one root object in each Bounded Context, which is called Aggregate. The same 'object' can exist in different BC, but will have a different name. Its identity will be kept via a unique id.
CQRS brings the concept of Commands being the most complex parts of your app, while Queries are usually very simple and don't require many layers.
What I like about the Clean Architecture is its focus on clear dependencies and on boundaries. Boundaries should be kept outside of your application. The communication between boundaries should happen via Data Transfer Objects. In the middle there's the Interactor, which represent a UseCase.
HexagonalJS is a result of inspiration from all of the above architectures. We took the UseCase/Context part from the DCI architecture with a little bit of the Clean Architecture. The idea of adapters is taken from the Hexagonal Architecture. The middle hex is often implemented using the building blocks taken from DDD. Our unique addition to this setup is a little bit of Aspect Oriented Programming.
Often, when I'm in doubt how to approach a new project, I'm trying to stand far from the Upfront Design. However, it doesn't hurt if I imagine the project in each of the architectures. This gives me new ideas about the domain I'm implementing.
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