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DDD Basics - Kortrijk Edition June 10, 2014 - Belgium @DDDBE — http://domaindriven.be

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Kindly hosted by

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We’ve got some great (international) speakers, but we need locations! ping @DDDBE http://domaindriven.be

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Aspects of Domain-Driven Design

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Tactical DDD ! design patterns

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Collaborative DDD ! model storming

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Strategic DDD ! complexity, scale

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Defining DDD (Yves) Ubiquitous Language (Jef) Bounded Contexts (Mathias) Context Mapping (Stijn) Modelling (Mathias) Starting/Selling DDD (Tom) Q&A / Lean Coffee

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Bounded Contexts

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“When something is wrong, something is too big.” — Leopold Kohr

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Large complex systems: harder to reason about

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Large complex systems: your mental model != my mental model

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Large complex systems: subtle nuances in meaning

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Avoid a big unified centralised model.

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Classic example: What is a product?

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Split into Bounded Contexts

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Make Bounded Context explicit pure independent consistent within its boundary

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Benefits: clarity model integrity freedom to evolve separately

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Drawbacks: short term convenience choosing the boundaries how big is the problem?

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Tricks

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Inspired by departments teams life cycles business processes

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What if this was an off-the-shelf solution?

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How much communication goes on between Bounded Contexts?

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Visualize! ! Context Mapping Model Storming

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Modelling

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Structural modelling describes state

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Structural modelling inspired by persistence concerns

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Relational Normalised CRUD Anaemic

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“CRUD is our industry’s grand failure.” — Greg Young

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Ask your Domain Expert about State Changes!

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Why does it change? When does it change? How often? Who causes it? By which rules? What consequences?

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! ! The moving parts are more interesting than the stable parts

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! ! A Domain Model is about:

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state + structure behaviour + change temporal roles + actors business rules + invariants causality + correlation interaction processes workflows + transitions intention + consequence failure …

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Modelling: Make the implicit explicit

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example ! Intentions: Command Objects Consequences: Domain Events

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Intention Protection Interpretation Automation user sends Commands manage processes domain model sends Events, guards consistency create read models from Events DTO Commands Events

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@mathiasverraes http://verraes.net