Vertical vs HorizontalSoftware Architecture

Christian HujerCEO / CTO Nelkinda Software Craft Pvt Ltd.

At RubyConf India 2016

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Horizontal Software Architecture

Directory structure reflects framework aspects� app/┣━� controllers/┣━� helpers/┣━� models/┣━� services/┗━� views/

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Why it’s called “horizontal”?

Because the predominant architecture represents (mostly) “horizontal” layers:

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views

helperscontrollers

services

models

Horizontal Architecture Synonyms

Horizontal ArchitectureLayered Architecturen-Tier ArchitectureMultitier ArchitectureTechnical Architecture

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Bad Horizontal - Fundamentals

● Cohesion● Coupling● Design Smells, Immobility● Communicating Intent● CCP - Common Closure Principle

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Cohesion

Things that change together are cohesive.

Examples:● A model, its view and and its controller.

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Collocation

Things which are “next” / “close” to each other.Examples:● Files in the same directory● Classes in the same package

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The 4 Design Smells (Uncle Bob)

Design smells are the odors of rotting software.

● Rigidity● Fragility● Immobility● Viscosity

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Immobility = Inability to Reuse

Reusable =● Independently deployable● Independently developable● Independently testable● Scalable (i.e. carving out microservices)

⇒ It’s important even if you don’t reuse!9@christianhujer @nelkinda #RubyConfIndia #Ruby 9

Oh, this is an MVC web application(Surprise, surprise!)

vs

Oh, this is an event registration system.

Software Architecture

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Communicate Intent!

Like every software entity,the architecture shouldcommunicate its intent,not its implementation!

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CCP: Common Closure Principle

“Classes that change together are packaged together.”

From the 11 (sic!) “SOLID” principlesDesign Principles and Design Patterns (Robert C. Martin, 2000)

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CCP: Cohesion Collocation Principle

Cohesive things should be collocated!

Put things that change together in the same place!

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Vertical Software Architecture

Directory structure reflects business aspects� app/┣━� attendee/┣━� event/┣━� organizer/┣━� payment/┗━� subscription/

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Vertical Software Architecture

Directory structure reflects business aspects� app/┣━� booking/┣━� cleaning/┣━� guest/┣━� payment/┗━� room/

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Let’s talk business!

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This talks Business!

� app/┣━� car/┣━� driver/┣━� insurance/┣━� rental/┗━� repair/

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This doesn’t talk Business!

� app/┣━� controllers/┣━� helpers/┣━� models/┣━� services/┗━� views/

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MVC is a pattern!Pattern ≠ Architecture

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Architecture /Directory Structure

Should ReflectThe Business Model

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MVC isn’t badBut…

it shouldn’t dominate you

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Vertical Software Architecture

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car driver insurance rental repair

Thank you!Follow me on Twitter

@christianhujer

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