Context

 @dataduke

As Developers... 

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Basics

 @dataduke

What is Event Storming?

• lightweight method to model a domain
  • within an event storming workshop we work in iterations to add layer by layer of elements to sharpen the picture of a domain
• typical elements
  • ​​domain events, commands, aggregates

  • issues/hot spots, chances

  • external systems, read models, policies

  • users/actors, timers, loops

Why do we use Event Storming?

• knowledge distribution
  • bring together people from different silos
  • domain experts/analysts/developers/architects
• enforcing a sharp timeline
  • experts will create locally ordered sequence of events
  • trigger long-awaited conversation
• following steps
  • structure will emerge
  • people and systems will be displayed
  • every layer sparkles a new type of conversation
  • ...

Iterations

 @dataduke

Phase: Kick-off

• Invite the right people (diversity in background/attitude, knowledge, curiosity)

• room setup (space to move, plenty of sticky notes/markers/food, timer)

• workshop structure (incremental notation, mostly stand-up, time-boxed warm-up e.g. Cinderella fairy tale story, explicit goal is to explore business process, uncomfortable/chaotic/awkward > take care of people, icebreaker)

Phase: Chaotic Exploration

product added to cart

• domain event (past tense)

• orange sticky note

• relevant for domain experts

Phase: Enforcing the timeline

• Make sure there’s enough space available

• Choose a sorting strategy (Pivotal Events, Swimlanes, Temporal Milestones, Chapters Sorting, or Combination)

• e.g. pivotal/Key Events: Article Added to Catalogue, Order Placed, Order Shipped, Payment Received and Order Delivered

Example (First Iteration)

Phase: Explicit walk-through

• ​talking about events while walking in front of the surface
• manage discussions (mark hot spots)
• telling the story backward (starting at terminal events)
• emerging consistent narrative

Phase: Problems and opportunities

• looking for key impediments, problems and opportunities (10-15 minutes time-box to capture risks and ideas)

Phase: Pick your problem

• arrow voting (target most important with e.g. 2x blue arrows per person)

First Iteration with all phases

Command-Event-Pairs

• command (present tense)

• blue sticky note

• triggers a domain event

product add to cart

Aggregates / Entities

• aggregate/entity

• yellow sticky note

• data that is interacted with

product

Borders & Flow

• find borders where a domain model has a different meaning

• domain events flow between different models

Bounded Contexts

• bounded context/sub-domain

• red sticky note

• core name that is relevant/valid

checkout

Outcome / Big Picture

• narrative/stories/user journey

• line(s)

• multiple storytellings

• common language for everyone

Example

More Elements...

Iterate / Color Puzzle Thinking

event

command

external system

policy

user

user

command

• add new colours/sticky notes: e.g. policies

• challenging value (discover new opportunities, inconsistencies)

• reveal pain points

• enable cross-perspective conversation

Example (End of Day 2)

Example (End of Day 2)

Patterns

• Add more space
• Be the worst
• Conquer first, Divide later
• Do first, Explain later
• Fuzzy Definitions
• Guess First
• Icebreaker
• Go Personal
• Keep your mouth shut
• Make some noise
• One man one marker
• The Right to be wrong
• ...

Anti-Patterns

• Ask questions first
• Big table at thhe center of the room
• Committee
• Do the right thing
• Dungeon Master
• Follow the leader
• Human bottleneck
• Religion war
• The spoiler
• Start from the beginning
• ...

Architecture

 @dataduke

Example

provider-ui

storefront-ui

merchant-ui

Frontend

api proxy

tenant

auth

Core

business unit

site

shop

Shop Admin

Product

product

. . .

. . .

. . .

. . .

Bounded Contexts > Microservices

Exe / Jar / Zip

Objects

Classes

OOP

Design Patterns

Modules

Layers

Project

Developer cares about ...

Strategic Design

Service

Domain

Domain-Driven-Design

Exe / Jar / Zip

Objects

Classes

OOP

Design Patterns

Modules

Layers

Project

Tactical Design

Upstream / Downstream

Call Flow

Model Flow

Context Map Patterns Categorized

Model Flow

 Upstream Patterns

• Open Host Service

• Event Publisher

 Downstream Patterns

• Customer / Supplier

• Conformist

• Anticorruption Layer

 In-Between Patterns

• Shared Kernel

• Published Language

• Seperate Ways

Upstream System

Down-stream System

provider-ui

storefront-ui

merchant-ui

Frontend

api proxy

tenant

auth

Core

business unit

site

shop

Shop Admin

Product

product

. . .

. . .

. . .

. . .

Microservices

Context Map

Strategic Design Tools

Tactical Design Tools

Building Blocks in DDD

Take-Aways

 @dataduke

Try Event Storming!

Ubiquitous Language

• use the same vocabulary for the same concepts
• e.g. domain experts, analysts, developers use same language to describe a problem on the whiteboard

Bounded Context

• area of the problem space where the ubiquitous language is valid
• e.g.
  • customer in sales = social interests, likes, needs
  • customer in support = history, tickets
  • customer in accounting = method of payment
  • customer in order = addresses, availability

Most important terms... I/II

Domain Model

• interpretation of reality
• includes the chosen aspects for implementation
• refers to the abstraction of the subdomain

Most important terms... II/II

A domain model is to a bounded context

what classes are to objects

Context Map

• relation between bounded contexts

References

• www.eventstroming.com
• www.leanpub.com/introducing_eventstorming
• www.youtube.com/watch?v=1i6QYvYhlYQ
• www.youtube.com/watch?v=lG46Yo_9DPc

For more Domain Modelling

 @dataduke

 Benjamin Nothdurft

 codecentric AG

 Developer Open Space

2019-10-11 in Leipzig

Jacek Bilski will rock on!

The End...

Facilitation

 @dataduke

Elements

Facilitation Hints

Text

• ​invite the right people
• room setup
• workshop structure (possible warm-up excercise: Cinderella etc.)

Process

Process

Actors & Policies

Let's start!

Exe / Jar / Zip

Objects

Classes

OOP

Design Patterns

Modules

Layers

Project

Developer cares about ...

Tactial Design

Service

Exe / Jar / Zip

Objects

Classes

OOP

Design Patterns

Modules

Layers

Project