Everyone is talking about bounded contexts, but nobody can agree on what they are. Are they microservices? Do they contain the UI? Do they exist in the real world? What if bounded contexts are actually an incredibly powerful tool for enabling your entire organisation to go faster?

1. #DDDesign @ntcoding
The Art of Discovering Bounded Contexts
Nick Tune
@ntcoding
ntcoding.co.uk/blog
ntcoding.co.uk

4. @ntcoding
Bounded Context Search Trends

5. @ntcoding
Source: Daily Mirror, April 2013

6. @ntcoding
“Microservices is a loosely-coupled,
service-oriented architecture with
bounded context
Adrian Cockroft
@adrianco

7. @ntcoding
“Microservices should cleanly align to
bounded contexts
Sam Newman
@samnewman

8. @ntcoding
Bounded contexts exist
in the real world!

9. @ntcoding
No. That’s Subdomains!

10. @ntcoding
No!

11. @ntcoding
Yes!

12. @ntcoding
Fine! Give me my
toys back then!

13. @ntcoding
“One Microservice should cover one
bounded context
-- Apium Tech
https://apiumtech.com/blog/domain-driven-design-distilled-by-vaughn-vernon/

14. @ntcoding
“Why is everyone so eager to establish
a 1:1 mapping between microservices
and bounded contexts!?
Alberto Brandolini
@ziobrando

15. Bounded contexts
do not own the UI!

16. Mine do!

17. You don’t know
what you’re talking
about

18. Eurgh.
Did you have a
Vindaloo last
night?

19. @ntcoding
Have bounded contexts become just a
pretentious buzzword that makes
people feel clever?

20. BE CAREFUL
WITH BOUNDED
CONTEXTS!

21. Discovering
Bounded Contexts
#1

22. @ntcoding
“Finding service boundaries is really damn
hard... There is no flowchart!
Udi Dahan
@udidahan

23. @ntcoding
Discover the Core
Business Model
Canvas
User research &
testing
Image: wikimedia

24. @ntcoding
Start by exploring core use
cases and processes

25. @ntcoding
Use Case: Renegotiating Property Tax
As an overpaying Ratepayer
I want to renegotiate my annual property tax
So that I am not unfairly losing money
Given ….
When ….
Then …..

26. @ntcoding
Use Case: Renegotiating Property Tax
Overpaying
Ratepayer
1. Review
existing
property tax
assessment
Assessment
Review
Surveyor
Survey property and
upload assessment
Attribute
Resubmit
2. Resubmit
incorrect
attribute(s)
3. Create
resubmit case
Case
Management
Caseworker
4. Review case
(14 day SLA)
5. Instruct re-survey

27. @ntcoding
Resubmit Case Management
Ratepayers Caseworkers
Review
Renegotiate
Context Map: Hypothesis
* This is not all of the contexts

28. @ntcoding
Clues for Discovering Contexts
- Linguistic boundaries
- Data: flow, ownership, uniqueness
- Domain expert boundaries
- Existing organisational boundaries**
- Business process steps

29. @ntcoding
“All models are wrong, some are useful.
-- George Box

30. HOW DO WE
KNOW WHICH
MODEL TO
CHOOSE?

31. Justifying
Bounded Contexts
#2

32. @ntcoding
Customers don’t care how
clean your pretty little
models are

33. @ntcoding
Resubmit Case Management
Ratepayers Caseworkers
Review
Renegotiate
Context Map: Organisational

34. @ntcoding
Composite Applications
Resubmit
Renegotiate
Review
Ratepayers Case workers
= Composite application

35. @ntcoding
Finding Service Boundaries: The One Rule
that Matters…
Maximise your ability to frequently deliver and
get feedback
ntcoding.co.uk/blog/2017/01/finding-service-boundaries-one-rule

36. @ntcoding
Good boundaries
improve flow. You
need to understand
Theory of Constraints.

37. @ntcoding
Resubmit Case Management
Ratepayers Caseworkers
Review
Renegotiate
Context Map: Bottlenecks

38. @ntcoding
DDD = model hypothesis
ToC = model validation

39. Evolving
Bounded Contexts
#4

40. @ntcoding
Boundaries must evolve.
New business, domain, and
technical insights challenge
existing assumptions

41. @ntcoding
“Trade off collaboration costs [between
teams] with innovation speed based on
current organisational needs
Matthew Skelton
@matthewpskelton

42. @ntcoding
Contexts Grow and Multiply
Discovery
(supportive)
becomes
Catalogue
(supportive)
Search
(supportive)
Recommend.
(Core)

43. @ntcoding
Context Cohesion
Search
Recommend.
Payments
Streaming

44. @ntcoding
Which Team(s) Builds the MVP?
Management
Context
Optimisation
ContextMVP

45. @ntcoding
Discovery Team & Highly-Aligned Tribe
Management
Context
Optimisation
Context
MVP
Campaigns
Tribe

46. GAMING CREATES MEGA ALIGNMENT

47. @ntcoding
Alignment Tricks for Devs
• Show and tells
• Cross-team pairing
• Cross-functional pairing
• Event storming

48. Rethinking
Bounded Contexts
#5

49. @ntcoding
Bounded contexts are a
proxy heuristic for…
Autonomy

50. @ntcoding
BoundedAutonomy Contexts
MS
UI
UI
Product and tech things
that change together for
business reasons, owned
by a single team.

51. @ntcoding
To be effective with DDD
you must be good at
organisation architecture

52. @ntcoding
“If the architecture of the organization is at
odds with the architecture of the system,
the architecture of the organization wins
--Ruth Malan
@ruthmalan

53. @ntcoding
What You Need to Do
- Experiment with models
- Learn Theory of Constraints
- Justify your choices with the one rule
- Strive for high alignment

54. @ntcoding

55. @ntcoding
The art of discovering
bounded contexts is the art
of aligning organisational
and technical boundaries.

56. @ntcoding
Next Steps…
- ntcoding.co.uk/blog/ddd
- Alignment at Scale - Henrik Kniberg
- scs-architecture.org
- Finding Service Boundaries - Udi Dahan
- ntcoding.co.uk/workshops
@ntcoding ntcoding