Date: May 2023 Speaker: Jakub Pillimon, Staff Technologist, VMware

1. JakubPilimon
pilo_dev
pilloPl
DOMAIN-DRIVEN DESIGN
THEORY VS PRACTICE

2. NO UPFRONT DEFINISIONS

3. DOMAIN-DRIVEN DESIGN?
DDD?

4. CLEAN CODE?

5. CLEAN ARCHITECTURE?

6. CLEAN MODEL?

7. WHAT IS A MODEL?

8. INFORMATION GATHERING

9. MODULARIZATION

10. EVENT STORMING
EVENT
EVENT EVENT EVENT

11. PIVOTAL EVENTS

12. WHAT IS „A DOCUMENT”?

13. A RICH OBJECT

14. AN ANEMIC OBJECT

15. A COMPRESSED DATA

16. BOUNDED CONTEXT

17. WHAT IS „A POLICY”?

18. PIVOTAL EVENTS

19. OTHER HEURISTICS

20. LANGUAGE

21. DEPARTAMENTS

22. SINGLE SOURCE OF TRUTH

23. GENERIC AND CORE
PROBLEMS

24. WHAT KIND OF CODE IS INA
BOUNDED CONTEXT?

25. WHAT IS AN AGGREGATE?

26. UNDERSTAND DIFFERENT
TYPES OF LOGIC

28. „Can’t spend more money
than you have”

29. AGGREGATE
COMMAND
CONSISTENCY

30. „After charging a payer, an
external legacy system must
be informed (unless it is
Friday)”

31. AGGREGATE
APPLICATION
SERVICE
INTEGRATION/APPLICATION
EXTERNAL
SYSTEM

32. „ISBN must be correct”

33. VALIDATION
COMMAND
API

34. „Order forms are grouped
into packages”

35. ASK QUESTION: „WHAT DOES IT
CHANGE?”
ORDER
ADDED TO
PACKAGE
ORDER
REMOVED TO
PACKAGE
SO WHAT? WHAT
HAS HAPPENED?

36. PRESENTATION LOGIC
READ MODEL

37. ASK QUESTION: „WHAT DOES IT
CHANGE?”
ORDER
ADDED TO
PACKAGE
ORDER
REMOVED TO
PACKAGE
ASSISTANT
(ASSIGNED TO
THE PACKAGE)
NOW HAS
PERMISSION TO
ALL THE FORMS
PERMISSION
TO FORMS
GRANTED

38. SLICING A PROCESS DOES
NOT ALWAYS WORK

39. E-Scooter riders place reservations.
Reservation contains a particular e-scooter’s id,
rider’s id and it’s valid for a speci
fi
c amount of time.
There can be only one reservation for a particular
e-scooter at any given point of time.
New reservations are active by default. They can
expire or be canceled.

40. E-Scooters must be maintained (for instance -
battery replacement)
E-scooters that are put into maintenance mode
can’t be reserved.
E-scooters which are reserved can’t be put into
maintenance mode

41. Sometimes we predict high demand for e-
scooters in particular zones (areas).
They are delivered to the zone and can’t be
reserved by riders until speci
fi
c time (can’t be
put into maintenance mode either)
We can’t use scooter for a demand if it is
reserved or currently in maintenance.

42. E-SCOOTER
SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DEMAND
(requested?)

43. E-SCOOTER
SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)

44. E-SCOOTER
SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)
Block
Block
Block

45. DEMAND
SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)
Blocked
Change description

46. POOR SCALABILITY

47. OR INCONSISTENCY

48. POOR TESTABILITY

49. COGNITIVE LOAD

50. DISPLAY
READY TO
RIDE
E-SCOOTERS

51. MAP SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)

52. PROBLEMATIC TEAM
DEPENDENCIES

53. HOW MANY TEAMS GET A
TASK TO DELIVER THAT
STORY?

54. MAP SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)

55. DRY
(LOGIC, NOT CODE!)

56. COUPLING

57. MAP SERVICE
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)
E-SCOOTER
SERVICE

58. LOGICAL COUPLING

59. E-SCOOTER
SERVICE isAvailable?
RESERVATION
(placed?)
E-SCOOTER
(under
maintenance?)
DE
DEMAND
(requested?)
Availability Model

60. E-SCOOTER
SERVICE
Implementation
detail
Implementation
detail
DE
Implementation
detail
OBSERVABLE
BEHAVIOR

61. E-SCOOTER
SERVICE
Implementation
detail
Implementation
detail
DE
Implementation
detail
OBSERVABLE
BEHAVIOR
MAP SERVICE

62. COUPLING TO
OBSERVABLE BEHAVIORS

63. COUPLING TO
IMPLEMENTATION DETAILS

64. CONTENT COUPLING

65. INFORMATION HIDING

66. HOW TO NOTICE IT IN
YOUR PROJECT?

67. ASK QUESTION: „WHAT DOES IT
CHANGE?”
RESERVATION
COMPLETED
E-SCOOTER
PUT INTO
MAINTAINEN
ACE MODE
DEMAND
REQUESTED
STATUS IN DB
CHANGED
THERE IS
RESERVATION
RECORD

68. ASK QUESTION: „WHAT DOES IT
CHANGE?”
RESERVATION
COMPLETED
E-SCOOTER
PUT INTO
MAINTAINEN
ACE MODE
DEMAND
REQUESTED
E-SCOOTER
UNAVAILABLE

69. ASK QUESTION: „WHAT ELSE CAN
HAVE THE SAME RESULT?”
RESERVATION
COMPLETED
E-SCOOTER
UNAVAILABLE

70. „DON’T COMPLICATE!”

71. „COMPLICATION” LEADS
TO PROPER
ABSTRACTIONS

72. E-SCOOTER
SERVICE
Implementation
detail - reason
Implementation
detail - reason
DE
Implementation
detail - reason
OBSERVABLE
BEHAVIOR
MAP SERVICE

73. RESERVATION
AND RIDING
MAINTENANCE DE
DEMAND
FORECAST
AVAILABILITY

74. UNDERSTAND UPSTREAM
VS DOWNSTREAM

75. SINGLE SOURCE OF
TRUTH

76. LOCATION
AVAILABILITY
Is it available? Where is it?
Take/release
Register
position

77. COHESION

78. NOT JUST LOGICAL
COHESION

79. Location Availability
E-Scooter E-Scooter
position takenTill

80. LOCATION
AVAILABILITY
DEMAND
REQUESTED
DEMAND
CANCELED
RESERVATION
COMPLETED
RESERVATION
CANCELED
RESERVATION
EXPIRED
PUT INTO
MAINTAINENC
E MODE

81. LOCATION
AVAILABILITY
SCOOTER
TAKEN/
RELEASED
DEMAND
…
RESERV
ATION…

82. UNDERSTAND PUBLISHED
VS PUBLIC

83. BE LIBERAL INSIDE,
STRICT ON THE OUTSIDE

84. E-Scooter riders place reservations.
Reservation contains a particular e-scooter’s id,
rider’s id and it’s valid for a speci
fi
c amount of time.
There can be only one reservation for a particular
e-scooter at any given point of time.
New reservations are active by default. They can
expire or be canceled.

85. WHAT IS A
„RESERVATION?”

86. RESERVATION
COMPLETED
E-SCOOTER
UNAVAILABLE
E-SCOOTER RESERVATION
JUST A CONSEQUENCE
DECISION EFFECT OF THE DECISION
AGGREGATE READ MODEL

87. FIND REAL CONCEPTS/
ABSTRACTIONS

88. OFTENTIMES USER
STORIES ARE JUST FULL
OF UI CONCEPTS

89. USER STORIES ARE JUST
THE BEGINNING OF A
CONVERSATION

90. JakubPilimon
pilo_dev
pilloPl
DOMAIN-DRIVEN DESIGN
THEORY VS PRACTICE