f you’re a software developer or architect who wants to play a more influential role in ensuring your software systems are optimised to support business goals, then you need to learn about the benefits and techniques of modern strategic domain-driven design. Many people think that DDD is about software design patterns, but that’s only a small part, and the least important part of DDD. In fact, Eric Evans wishes he’d focused more on the strategic aspects of DDD in his famous book (Domain-Driven Design: Tackling Complexity in the Heart of Software) and pushed the tactical coding patterns to the back! Strategic domain-driven design is about truly understanding the business domain. It involves collaboratively modelling business processes using advanced modelling techniques, like Event Storming and Domain Storytelling, with domain experts on an ongoing basis. One of the core outcomes of strategic DDD is identifying cohesive modules, known as bounded context. Bounded contexts help you to create a maintainable, comprehensible codebase by isolating dependencies and delineating concepts that reference different classes of business value. In this talk, you’ll see many of the most effective bounded context design heuristics, recurring patterns in the wild, and you’ll learn how to facilitate those vital modelling sessions so you can lead the adoption of strategic DDD in your organisation. More details: https://confengine.com/agile-india-2019/proposal/8100/strategic-domain-driven-design Conference link: https://2019.agileindia.org

1. Strategic Domain-Driven Design
Designing Sociotechnical Systems for
Continuous Delivery
Nick Tune | @ntcoding

2. CONTINUOUS DELIVERY
FEELS LIKE A DREAM

3. THE NIGHTMARE PROJECT

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“Can’t you just add a text box?”
Website
Digital Enterprise IT
Business
APIs
Data
APIs
Rules,
BPM,
ESB
Back
Office
Website
Website

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“A loosely coupled software
architecture and org structure to
match” is a key predictor of:
1. Continuous Delivery Performance
2. Ability to scale org and increase
performance linearly

6. “
ntcoding
[In our study at Thoughtworks we
found] work takes an order of
magnitude longer when it leaves a
team.
— James Lewis (@boicy)

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STRUCTURAL ISSUES ARE A TOP
HURDLE TO MEETING DIGITAL GOALS
https://www.mckinsey.com/business-functions/digital-mckinsey/our-insights/the-digital-tipping-point-mckinsey-global-survey-results

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How do we design
sociotechnical systems
(software and teams) to
maximise iteration quality
and speed?

9. “
ntcoding
the key to incremental architecture is
to build on a framework that can
accommodate change… that
framework is the domain.… By
modeling the domain, you can more
easily handle changes to the domain
— Allen Holub (@allenholub)

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“How hard can it be?”
https://segment.com/blog/goodbye-microservices/

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“How hard can it be?”
https://segment.com/blog/goodbye-microservices/
Service boundaries
causing barriers
…This led to developers
complaining of their service being
blocked by tasks on other
services and refusing to help out
by working with these blocking
tasks…

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HOW TO GROUP DOMAIN CONCEPTS?

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TAXONOMIES, TOPOLOGIES…
Group by
characteristic 1
(shape)
Group by
characteristic 2
(colour)
Group things which
must be used together
in a process

14. Fruit or vegetable?

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IS TOMATO FRUIT OR VEGETABLE?
Tomato is a fruit!
Scientifically, it
matches the
botanical definition
of a fruit.
?
VegetablesFruits
🍏
🍌
🍓 🥕🥦
🥔

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ntcoding
The U.S. Supreme Court ruled in 1893 in the
case Nix v. Hedden that tomatoes count as
vegetables — despite the botanical fact
that they're fruits.
...a tariff was put in place to protect domestic
vegetable growers by taxing imported
vegetables.
https://www.goodhousekeeping.com/home/gardening/a20705757/are-tomatoes-legally-a-vegetable/

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DOMAINS ARE FUZZY & CONTEXTUAL
Science context
Fruits Vegetables
Cooking context
Fruits Vegetables

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DOMAIN MODELLING FUNDAMENTALS
1. Many ways to model every domain
2. ‘Obvious’ models can be wrong
3. Context defines utility of model
4. Language is contextual

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STRATEGIC DOMAIN-DRIVEN DESIGN
Find bounded contexts - independent parts
of the domain.
Look for parts of the domain where
language has specialised meaning
(e.g. tomato) to identify bounded contexts.

20. Domain
SPORTS EQUIPMENT ECOMMERCE

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BOUNDED CONTEXTS
Catalogue
Product
- description
No shared code. No shared database.
No canonical data model. 1 team per BC.
Reviews
Product
- rating
Pricing
Product
- price
Inventory
Product
- stock
Inventory
Catalogue
Reviews
Pricing
Product

22. #1 Domain Discovery

23. EVENT STORMING

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MODEL DOMAIN AS A TIMELINE
CFP
Opened
Talk
proposal
submitted
CFP Closed
Talk
Accepted

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INCREMENTALLY ADD MORE DETAIL
CFP
Opened
Talk
proposal
submitted
CFP Closed
Proposal
Limit Policy
SpeakerChair
CFP Aggregation
System

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leanpub.com/introducing_eventstorming
eventstorming.com
github.com/mariuszgil/awesome-eventstorming

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EXPLORING BOUNDARIES WITH
EVENT STORMING
Alberto Brandolini: Discovering Bounded Contexts with Event Storming
Published in: DDD The First 15 Years (Leanpub)

28. #2 Bounded Context
Design Heuristics

29. Domain
FINANCIAL PRODUCTS

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BOUNDED CONTEXT DESIGN HEURISTIC
1. ALIGN WITH DOMAIN LANGUAGE
💰 Tier 1 Products
💰💰 Tier 2 Products
💰💰💰 Tier 3 Products
Credit Cards Mortgages Loans

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To design the optimal
architecture, you need to
know the business model.

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LEARN THE BUSINESS MODEL

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Decouple high value and low
value parts of the system to
maximise iteration speed
where ROI potential is
greatest.

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BOUNDED CONTEXT DESIGN HEURISTIC
2. ALIGN WITH VALUE
Tier 3
Products
(core)
Financial
Advice
(supportive) Payments
(generic)

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BOUNDED CONTEXT DESIGN HEURISTIC
3. OPTIMISE FOR SOCIAL NEEDS
Design systems so that the people
building them are motivated and
productive.
✅ Purpose ✅ Autonomy ✅ Mastery

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SOCIAL COMPLEXITY & COGNITIVE LOAD
If teams are too small, the chance of
dependencies between teams will be
greater.
If teams are too big, social complexity will
lead to burn out.

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BOUNDED CONTEXT DESIGN HEURISTIC
4. RESPECT TECHNICAL CONSTRAINTS
DDD does not mean ignoring
technical concerns and creating
pretty models.
Technical concerns should influence
your bounded contexts.

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RESPECT TECHNICAL CONSTRAINTS
• Legacy
• Performance
• Scalability
• Security
• Storage

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BOUNDED CONTEXT DESIGN HEURISTIC
5. DON’T IGNORE THE UX
UI UIUI
API API API
UI
API API API
Greater autonomy can result in a fractured user experience

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5 KEY HEURISTICS
1. Align with domain language
2. Align with business value
3. Optimise for social needs
4. Respect technical constraints
5. Don’t ignore the UX

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STRATEGIC DESIGN SCORECARD
This is a hypothetical illustration. The scores will
differ in different domains and organisations.
Assess your bounded
contexts against the 5
primary criteria for defining
boundaries.

42. #3 Strategic Design
Patterns

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PATTERNS
Useful
Apply learnings from one
situation to another
A starting point
Develop analytical mindset to
identify design trade-offs in
any situation
A shared language for
discussing similar challenges
Dangerous
No two situations are ever
exactly the same
A complete solution
Develop lazy mindset of just
using what worked before
without thinking
We think we’re talking about
the same thing but we aren’t

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Use the business process
pipeline pattern as a starting
point for modelling.

45. Domain
SMART CITIES / URBAN FURNITURE

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BUSINESS PROCESS PIPELINE
Street Sofa
Provisioning
Street Sofa
Activation
Street Sofa
Management

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Look for pivotal events -
significant business
occurrences indicating a
change in context or phase.

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PIVOTAL EVENTS
Street Sofa
Provisioned
Street Sofa
Activated
Street Sofa
Manufactured

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Never stop at the first design.
Try switching from business
process pipeline to capability
slices.

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PROCESS VS CAPABILITY SLICES
Furniture
Control
Citizen
Guidance
Smart
Advertising
Provision
Activate
Manage

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Align by process or
capabilities?
Use the strategic design
scorecard.

52. Domain
COMMERCIAL AIRLINE PLANNING

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BUSINESS PROCESS PIPELINE?
Calculate
Journeys
Routing
Staff
Allocate
Planes
Assign
Crews
Fleet
Staff
Crew
Staff

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DATA INVALIDATED - FIX IN-PLACE
Calculate
Journey
Routing
Staff
Allocate
Plane
Assign
Crew
Fleet
Staff
Crew
Staff
Legs
Cancelled
Plane
Damaged
Air
Hostess
Resigned

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BRAIN CONTEXT (ANTI PATTERN?)
Calculate
Journey
Routing
Staff
Allocate
Plane
Assign
Crew
Fleet
Staff
Crew
Staff
Rules 🧠

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BRAIN CONTEXT
• Sucks logic from other contexts
• Other contexts become tightly coupled
• High rate of co-change
• Teams coupled + politics
• Not always an anti-pattern

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Don’t confuse user journeys
and organisation structure
with domain processes.

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PROPOSAL PIPELINE
Calculate
Journey
Allocate
Plane
Assign
Crew

59. Domain
CONNECTED VEHICLES

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GATEWAY INTERCHANGE CONTEXT
Car Protocol
Translation
Bike Protocol
Translation
Boat Protocol
TranslationGateway
Interchange
Context
Location
Tracking
Device
Configurator
Component
Monitoring
Remote
diagnostics
Command

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HOMOGENOUS OCTOPUS CONTEXT
GDPR

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Analyse patterns using the
primary heuristics.

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HOMOGENOUS OCTOPUS CHARACTERISTICS
1. Value
Cost-efficiency/risk reduction over autonomy
2. Social
Huge inertia to required/breaking changes
3. Technical
Reduce burden on clients, centralise complexity

64. Domain
DIGITAL MUSIC STREAMING

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AUTONOMOUS CONTEXTS & MICRO-FRONTENDS
Search
UI UI UI UI
API API API API
Catalogue Reviews Player
Composite
web page

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DOGFOOD CONTEXT
Music Streaming Platform
External white label
Internal team

67. #4 Relationship Patterns

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Bounded contexts will always
have dependencies.
Relationship patterns help us
choose the most effective
collaboration approaches.

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CLASSIC DDD RELATIONSHIP PATTERNS
Shared Kernel Customer
Supplier
Open Host
Service
Conformist
OH
SK
C
S
🤝
Each pattern has technical and social/political characteristics
Anti-
corruption
Layer
ACL

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MODERN RELATIONSHIP PATTERNS
1. Inner Sourcing (internal open source model)
2. People rotation (temporary move to another team)
3. Sub-teams (fluid smaller teams within larger team)
4. Partnership Patterns (ways to group teams)
5. Alliance Teams (temporary new teams)

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SEMI-FLUID SUB-TEAMS
Sub-team 1
Sub-team 2 Sub-team 3
Sub-team 4
Static team lead
Rotating developer
Typically 1 developer
rotates per-team per-
month

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BEGRUDGING PARTNERSHIP
We’re stuck together but we want to go separate ways!
😡 😭

73. Domain
ADTECH / MARTECH

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ALLIANCE TEAMS
New ad platform
alliance
Campaign
Build
Campaign
Management
Temporary teams formed to solve a shared common goal
Campaign
Analytics

75. #5 Welcome to the DDD
Club…

76. DDD is not sacred rituals

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OTHER STRATEGIC DDD TOPICS
1. Evolutionary sociotechnical patterns
2. Large-scale design / superstructure
3. Context mapping
4. Classifying bounded contexts
5. Technical integration patterns

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MORE PATTERNS AND HEURISTICS
ntcoding.co.uk/sociotechnical
ntcoding.co.uk/blog
ntcoding.co.uk/speaking
@ntcoding
/in/ntcoding