ddd reboot (english version)

#DDDREBOOT

LET’S REBOOT DDD!THOMAS PIERRAIN - JEREMIE GRODZISKI @TPIERRAIN - @JGRODZISKI

#DDDREBOOT

LET’S REBOOT DDD!THOMAS PIERRAIN - JEREMIE GRODZISKI @TPIERRAIN - @JGRODZISKI

#DDDREBOOT

BEFORE WE BEGIN

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DDD AROUND YOU?OK, BUT 13 YEARS AFTER…

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THERE MUST BE A REASON…

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« TACTICAL PATTERNS », « BOUNDED CONTEXTS », « UBIQUITOUS LANGUAGE », ETC.

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DOES IT NOT MEAN ANYTHING TO YOU?

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ACTUALLY DDD…

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DOMAIN DRIVEN DESIGN, IS…

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TO FOCUS ON BUSINESS VALUE

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OUR FIRST WORK AS DEVELOPER?

UNDERSTAND THE DOMAIN THAT WE’LL HAVE TO CODE

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A SET OF CONCEPTS THAT, THROUGH USE CASES, ALLOWS US TO SOLVE PROBLEMS

DOMAIN?

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DOMAIN: DOUBLE ENTRY ACCOUNTING

SOLVED PROBLEMS: TRACKING, ROBUSTNESS

CONCEPTS: ACCOUNT, DEBIT, CREDIT, AMOUNT, ETC.

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DOMAIN: IDE

SOLVED PROBLEMS: PRODUCTIVITY, INTEGRATION

CONCEPTS: PROJECTS, FILES, ANALYSIS, REFACTORING, CVS, DEBUGGER, ETC.

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BUT DDD IS MOSTLY…

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AS DEVELOPERS, WE FACE …

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3 LEVELS

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IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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LEVEL 1 IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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QUESTION:

WHAT’S THE FOLLOWING CODE DOES?

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SO?

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DID YOU SEE SOME CODE SMELLS?

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Good code / Bad code

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#1 MAGIC NUMBERS

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#1 MAGIC NUMBERS #2 DUPLICATIONS

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#1 MAGIC NUMBERS #2 DUPLICATIONS #3 PRIMITIVE OBSESSION

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#1 MAGIC NUMBERS #2 DUPLICATIONS #3 PRIMITIVE OBSESSION #4 MIXED CONCERNS (TECH-BIZ)

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#1 MAGIC NUMBERS #2 DUPLICATIONS #3 PRIMITIVE OBSESSION #4 MIXED CONCERNS (TECH-BIZ) #5 FUZZY TERMINOLOGY

(

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AND NOW CONCERNING THE DOMAIN…

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LET’S FIND THE IMPLICITS !

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FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

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FIXED SHIPMENT COST?

FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

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FIXED SHIPMENT COST?

FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

WEIGHT IN G? VARIABLE COST FOR EACH SENT KG?

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CURRENCY IN EUROS?

FIXED SHIPMENT COST?

WEIGHT IN G? VARIABLE COST FOR EACH SENT KG?

FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

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CURRENCY IN EUROS?

FIXED SHIPMENT COST?

WEIGHT IN G? VARIABLE COST FOR EACH SENT KG?

SHIPPING OPTION?

FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

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CURRENCY IN EUROS?

FIXED SHIPMENT COST?

WEIGHT IN G? VARIABLE COST FOR EACH SENT KG?

SHIPPING OPTION?

FREE SHIPPING IF GREATER THAN 100? 100 WHAT?

VARIABLE COST PER PRODUCT CATEGORY?

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MAKE THE IMPLICIT, EXPLICIT

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DDD VERSION#DDDREBOOT

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VALUE TYPE

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THE VALUE TYPE EXPRESS YOUR DOMAIN AND

SWALLOW YOUR COMPLEXITY

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-VALUE TYPES- IT'S WHAT THEY ARE THAT IS IMPORTANT;

NOT WHO THEY ARE

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-VALUE TYPES- Σ OF ATTRIBUTES MEANING

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-VALUE TYPES-Example

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-VALUE TYPES-A COLOR (RGB: 255-255-0)

A SPEED OF 50 KM/H A BANK NOTE OF 10 €

Examples

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-VALUE TYPES- IMMUTABLES BY DEFINITION RICH WITH DOMAIN LOGIC EQUALITY ON ATTRIBUTES

COMPOSABLES (OPERATORS, FONCTIONS) AUTO-VALIDATING

Characteristics

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-VALUE TYPES- “TRANSACTIONAL” CONSTRUCTOR OR OPERATION

CONSTRAINTS ENFORCED BY THE CONSTRUCTOR, NOT BY THE OPERATIONS

FAIL FAST NO SETTERS !

IMMUTABILITY, AUTO-VALIDATING

Implementation

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-VALUE TYPES- Implementation

RICH WITH DOMAIN LOGIC

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-VALUE TYPES- ON ALL THE ATTRIBUTES!

Implementation

STRONG UNICITY

hashCode

STRONG EQUALITY

equals

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-VALUE TYPES- “SIDE-EFFECT FREE” FUNCTIONS

out of the tar pit

WE COMPOSE, AND PREFER RÉ-ASSIGNING

INSTEAD OF CHANGING THE STATE LIKE BEFORE :-(

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ESSENTIAL COMPLEXITY ACCIDENTAL COMPLEXITY

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« VALUE OBJECT »#DDDREBOOT

IN DDD, WE NAME THAT:

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« VALUE OBJECT »#DDDREBOOT

IN DDD, WE NAME THAT:

OXYMORON

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-VALUE TYPE- ELECTED BEST R.O.I. OF DDD LAND

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EXPRESS THE DOMAIN CODEBASE PROGRESSIVE INTRODUCTION / EXEMPLARY

COMPLEXITY SWALLOWER SIMPLIFY REASONING

(IMMUTABLE, THREAD-SAFE, TESTABLE)

- VALUE TYPE - AN UNBEATABLE R.O.I.

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PLANT THE SEED OF THE DOMAIN INTO THE CODE

THE VALUE TYPE

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MAKE THE IMPLICIT, EXPLICIT

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SHIPPING COST DECISION TABLE

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SHIPPING COST DECISION TABLE

DATA LITERALS!

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AND, AS WE TALK ABOUT IMPLICIT…

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"I CAN'T LISTEN TO THAT MUCH WAGNER. I START GETTING THE URGE TO CONQUER

POLAND" (WOODY ALLEN)

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“I CAN’T SEE THAT MUCH MANAGERS IN CODE.

I START GETTING TO…» (JÉRÉMIE)

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SHOOT THE MANAGERS!

;-)

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MAKE THE IMPLICIT, EXPLICIT

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ANOTHER PROBLEM

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LOST IN TRANSLATION#DDDREBOOT

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"IT'S DEVELOPER'S UNDERSTANDING, NOT YOUR KNOWLEDGE THAT BECOMES SOFTWARE!"

Alberto BRANDOLINI (facing non collaborative BAs)

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IN SOME CASES…

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SOLUTION?

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SOLUTION?

1 LANGUAGE : YOUR USERS’S ONE!

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« THE UBIQUITOUS LANGUAGE »#DDDREBOOT

IN DDD, IT’S NAMED:

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YES BUT, HOW DO WE DO WHEN…

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A « CUSTOMER » IT'S…

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SO, HOW DO WE DO?

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CONTEXT MATTERS

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CONTEXTA GROUP OF PERSONS SHARING THE SAME

MEANING BEHIND WORDS.

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Context

CRM / Sales

Customer => Socio-Economic group & Center of Interest

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Context Accounting

Customer  => Method of & Payment Period

Context

CRM / Sales

Customer => Socio-Economic group & Center of Interest

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Context

Order-Shipment

Customer  => addresses, availability

Context Accounting

Customer  => Method of & Payment Period

Context

CRM / Sales

Customer => Socio-Economic group & Center of Interest

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« BOUNDED CONTEXT »#DDDREBOOT

IN DDD, WE NAME THAT:

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CRM / Sales Context

Model and Language of Sales

Orders / Shipment

Context

Model & language of Logistics

Accounting Context

Model and Language of Accounting

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CRM / Sales Context

Model and Language of Sales

Orders / Shipment

Context

Model & language of Logistics

Accounting Context

Model and Language of Accounting

APP UI

WEB API

DATABASES APP UI

APP UI

APP UI DATABASES

WEB API

APP UI

APP UI

DATABASES

BATCH

USERS MANUAL

USERS MANUAL

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CONTEXT PRODUCTS CATALOG

CONTEXT « SEARCH »

CONTEXT CLIENT & ORDERS

ADS CONTEXTCONTEXT “RECOMMANDATIONS"

CONTEXT « PROMOTIONS »

CONTEXT « PRODUCT HIGHLIGHTING »

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LEVEL 2 IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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PROBLEM

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ONE THING CHANGES AND…

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WHY SO MUCH DOMAIN TECHNICAL

STUFF IN OUR CODEBASE?

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SOLUTION? HEXAGONAL

ARCHITECTURE

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THE WORLD DIVIDES IN 2 CATEGORIES…

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OUTSIDE

INSIDE

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DOMAIN

INFRA (HTTP, Db, MoM,…)

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DOMAIN CODE

DO NOT ENTER BUSINESS CODE

ONLY

INFRA CODE (Ports & Adapters DMZ)

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DOMAIN CODE

DO NOT ENTER BUSINESS CODE

ONLY

INFRA CODE >> playground <<

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OUTSIDE

INSIDE

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HEXAGONAL ≠ LAYERS

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LAYERS ARCHITECTURE+—————————+ | PRESENTATION | +—————————+ | DOMAIN | +—————————+ | DATABASE | +—————————+

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+———————————————+ | PRESENTATION | DATABASE | … | +———————————————+ | DOMAIN | +———————————————+

HEXAGONAL ARCHITECTURE

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« Hexagonal Architecture ?!?

(…) That pattern is

fucking awesome! »

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ANOTHER PROBLEM

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LEGACY NAM’

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LEGACY NAM’

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LEGACY NAM’

(WAGNER’S VERSION)

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THE RECURRING QUESTION: DO WE REBUILD

EVERYTHING FROM SCRATCH OR NOT?

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Legacy Application

Context

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Legacy Application

ContextWell-crafted DDD

Bubble Context

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Well-crafted DDD

Bubble Context

ANTI-CORRUPTION LAYER

Legacy Application

Context

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LEVEL 3 IS / COMPANY

APPLICATION / TEAM

CODE / PAIR

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THE PROBLEM

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EVEN FOR

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RELATIONS BASED ON POWER

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MAKE THE IMPLICIT, EXPLICIT

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CONTEXT MAP EXPLICITS THE RELATIONS OF “POWER”

BETWEEN TEAMS

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UPSTREAM / DOWNSTREAM

« IF YOU ARE UPSTREAM AND YOU POLLUTE THE RIVER… … PEOPLE DOWNSTREAM

WILL BE IMPACTED. NOT THE INVERSE. »

METAPHOR OF THE RIVER FLOW

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« Search »

Context

Upstream

downstream

Products Catalog

Context

CONTEXT MAP

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« Search »

Context

U

d

Products Catalog

Context

CONTEXT MAP

ANTI-CORRUPTIO

N LAYER

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UPSTREAM / DOWNSTREAM CUSTOMER - SUPPLIER

CONFORMIST

ANTI-CORRUPTION LAYER (ACL) SERVICE HOST

SHARED KERNEL …

SOME VOCABULARIES AND PATTERNS

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« CONTEXT MAP & STRATEGIC DESIGN »

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IN DDD, WE NAME THAT:

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SO…

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BEFORE LEAVING

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DOMAIN DRIVEN DESIGN, IS…

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A LOT MORE ACCESSIBLE & USEFUL THAN IT MIGHT SEEMS

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STARTING MONDAY

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Ubiquitous Language

Value types

Entities

Aggregates

Repositories

Factories

Services

Domain Events

Model Driven Design

Core Domain / Generic Subdomains

Hexagonal Architecture*

CQRS*

Event Sourcing*

Bubble Context

Bounded Contexts

Context Maps

Anti-corruption Layer

Event storming

Customer / Supplier

Distillation

Shared Kernel

Conformist

…

CODE LEVEL

APP LEVEL

ENTREPRISE LEVEL

DDD BUILDING BLOCKS

* : not DDD but friendly

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ON THE SHOULDERS OF GIANTS

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THANK YOU ERIC !

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BUT SOMETIMES…

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LET’S REBOOT DDD!

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LET’S REBOOT DDD!AN OPEN COMMUNITY OF PRACTITIONERS

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LET’S REBOOT DDD!AN OPEN COMMUNITY OF PRACTITIONERS

1. POPULARISING DDD BY BEING MORE ACCESSIBLE JARGON

#DDDREBOOT#DDDREBOOT

LET’S REBOOT DDD!AN OPEN COMMUNITY OF PRACTITIONERS

1. POPULARISING DDD BY BEING MORE ACCESSIBLE JARGON

2. CONTINUE TO ENRICH THE DDD TOOLBOX

#DDDREBOOT#DDDREBOOT

LET’S REBOOT DDD!1. POPULARISING DDD BY BEING MORE ACCESSIBLE JARGON

2. CONTINUE TO ENRICH THE DDD TOOLBOX

AN OPEN COMMUNITY OF PRACTITIONERS

#DDDREBOOT#DDDREBOOT

LET’S REBOOT DDD!

@DDDreboot +

ALL TOGETHER

LET’S MAKE DDD MAINSTREAM

#DDDREBOOT#DDDREBOOT

LET’S REBOOT DDD!1. POPULARISING DDD BY BEING MORE ACCESSIBLE JARGON

2. CONTINUE TO ENRICH THE DDD TOOLBOX

@DDDreboot +

AN OPEN COMMUNITY OF PRACTITIONERS