Event Storming (P. Rayner)

1. COLLABORATIVE LEARNING
FOR COMPLEX DOMAINS
EVENTSTORMING
@thepaulrayner
Paul Rayner

2. THE LANDSCAPE
Complex business rules &
processes
Knowledge silos
Numerous diverse (& often
legacy) system interactions

3. THE CRITICAL COMPLEXITY OF MOST
SOFTWARE PROJECTS IS IN
UNDERSTANDING THE DOMAIN
ITSELF
Eric Evans

4. HTTPS://EN.WIKIPEDIA.ORG/WIKI/ROSETTA_STONE#/MEDIA/FILE:ROSETTA_STONE.JPG

5. HOW DO WE LEARN
…FAST?

7. https://www.drupal.org/node/1785994

8. BEHAVIOUR TRUMPS
STRUCTURE

9. https://commons.wikimedia.org/wiki/File:Use_case_restaurant_model.svg

10. https://commons.wikimedia.org/wiki/File:Activity_conducting.svg

11. https://commons.wikimedia.org/wiki/File:CheckEmail.svg

12. OPTIMIZE FOR
SHARED LEARNING

13. leanpub.com/introducing_eventstorming

14. PLACE EVENTS ON
A TIMELINE

15. leanpub.com/introducing_eventstorming

16. WHAT IS A DOMAIN EVENT?
Something that happened
in the business
that your domain experts
care about

17. leanpub.com/introducing_eventstorming

18. SPECIES OF DOMAIN EVENTS
• A step in a business process
e.g. customer order submitted, customer paid $100, order
completed, item shipped.
• Something that happens on a scheduled basis
e.g. nightly account reconciliation completed, end of month.
• Something meaningful that occurs as a
result of something else happening
e.g. customer account locked after invalid password
entered 3 times

19. VISUALIZE
LEARNING
OPPORTUNITIES

21. leanpub.com/introducing_eventstorming

22. leanpub.com/introducing_eventstorming

23. EVENTS &
QUESTIONS FIRST

26. EVENTSTORMING
A LEGACY APPLICATION

29. PROVIDE UNLIMITED
MODELING SPACE

32. leanpub.com/introducing_eventstorming

33. leanpub.com/introducing_eventstorming

34. They lived
happily ever
after
Once
upon a
time… More modeling space than you expect

35. INVITE THE RIGHT
PEOPLE

36. Development team members and business people
gather in a room and together we create a visual map
of the flow of events

37. EVENTSTORMING
IN ACTION

41. VISUALIZE
INTERACTIONS

42. leanpub.com/introducing_eventstorming

43. leanpub.com/introducing_eventstorming

44. leanpub.com/introducing_eventstorming

45. VISUALIZE
BUSINESS RULES

46. leanpub.com/introducing_eventstorming

47. PROVIDE A
VISIBLE LEGEND

51. Adapted from leanpub.com/introducing_eventstorming

52. VISUALIZE
ALTERNATE FLOWS

53. Decided to Reimburse (alternate flow)
Decided to Repair (main flow)

54. NATURAL TRANSITION
TO EVENT SOURCING

55. Adapted from leanpub.com/introducing_eventstorming

56. EVENT SOURCING

57. Shopping Cart
Item
Added
ECommerce Context
Price
Calculated
Promotion
Code
Applied
Item
Added
Price
Calculated
Checked
Out
Aggregate state modeled as a sequence of domain events

58. EVENT SOURCING
‣ Don't save the current state of objects
‣ Process events that lead to the current state
‣ TDD focused on command processing
generating the correct events

59. CLARIFYING CONTEXT
BOUNDARIES

60. Servicer Management Context
Claims Context

61. NATURAL TRANSITION TO
DISTRIBUTED SYSTEMS

62. Event Stream
…
ECommerce Context
Event Stream
…
Order Management
Context

63. FACILITATION TIPS

64. EVENTSTORMING FACILITATION TIP #1
Focus first on
learning and
understanding

65. CLARIFYING QUESTIONS
‣ “What circumstances would cause ... to
happen?”
‣ “What was the path that led us here?”
‣ “What is a good example of …?”

66. CLARIFYING QUESTIONS
‣ "What do you mean by …?"
‣ "What might lead someone to do/need …?”
‣ "What else might happen…?

67. EVENTSTORMING FACILITATION TIP #2
Anchor to a
concrete business
example

68. EVENTSTORMING FACILITATION TIP #3
Clarify fuzzy
concepts and
language

69. Command is “Open Claim”
What should associated
event be called?

70. EVENTSTORMING FACILITATION TIP #5
Conversations
and examples are
primary

71. EVENTSTORMING FACILITATION TIP #6
Post first,
Ask questions
later

72. EVENTSTORMING FACILITATION TIP #4
Timebox

74. POSSIBLE LIMITATIONS
‣ Simple business domains (e.g. CRUD)
and/or systems
‣ Distributed teams
‣ Larger group/greater complexity =
better facilitation
‣ ???

75. WHY
EVENTSTORMING?

77. WHY EVENTSTORMING?
Collaborative learning
Cultivate mutual shared
understanding
Uncover misunderstandings & missing
concepts
Avoid rework

78. WHY EVENTSTORMING?
Model & explore complex
domains
Visual, tactile representation of system
behaviour & outcomes
Smoother transition to a rich domain
model, design and coding

79. QUESTIONS?
@thepaulrayner
Paul Rayner

80. THANKS!
@thepaulrayner
Paul Rayner