Domain-driven design is a collaborative process involving both domain experts and software practitioners. This high-level overview takes a look at the driving principles behind domain-driven design. It also explores domain-driven design's building block patterns, supple design, strategic design, and distillation of the core.

1. Domain-Driven Design
A Collaboration Between
Domain Experts and Software Practitioners

2. The Book
http://domaindrivendesign.org/books/evans_2003

3. do·main
dōˈmān n.
a sphere of knowledge,
in uence, or activity
"domain." Merriam-Webster.com. 2011. http://www.merriam-webster.com/dictionary/domain (17 October 2011).

4. Core Domain

5. Core Domain
• complexity is in the domain, not the technology

6. Core Domain
• complexity is in the domain, not the technology
• let technology play a supporting role

7. Core Domain
• complexity is in the domain, not the technology
• let technology play a supporting role
• uncover your core domain and distill this core

8. The Model*
*In domain-driven design, the model is not the classes or objects representing concepts within the model.

9. The Model*
• a model is a tool for solving speci c problems within a domain
*In domain-driven design, the model is not the classes or objects representing concepts within the model.

10. The Model*
• a model is a tool for solving speci c problems within a domain
• “the map is not the territory” —Alfred Korzybski
*In domain-driven design, the model is not the classes or objects representing concepts within the model.

11. The Model*
• a model is a tool for solving speci c problems within a domain
• “the map is not the territory” —Alfred Korzybski
• collaborative explore the model with both domain experts
and software practitioners
*In domain-driven design, the model is not the classes or objects representing concepts within the model.

12. Bounded Context

13. Bounded Context
• there are always multiple models

14. Bounded Context
• there are always multiple models
• explicitly de ne a bounded context to which a model applies

15. Bounded Context
• there are always multiple models
• explicitly de ne a bounded context to which a model applies
• speak a ubiquitous language within a bounded context

17. Building Blocks

18. Entity

19. Entity
• de ned by a thread of continuity and identity

20. Entity
• de ned by a thread of continuity and identity
• only responsibilities should be around identity and life cycle

21. Entity
• de ned by a thread of continuity and identity
• only responsibilities should be around identity and life cycle
• may be composed of other entities and/or value objects

22. Value Object

23. Value Object
• de ned by its encapsulated attributes

24. Value Object
• de ned by its encapsulated attributes
• treat value objects as immutable

25. Value Object
• de ned by its encapsulated attributes
• treat value objects as immutable
• delegate business logic to value objects

26. De ning an object as an entity or a
value object is context-dependent.

27. Aggregate

28. Aggregate
• a group of related entities and value objects

29. Aggregate
• a group of related entities and value objects
• useful when de ning transaction, distribution and
concurrency boundaries

30. Aggregate
• a group of related entities and value objects
• useful when de ning transaction, distribution and
concurrency boundaries
• designate one entity as the aggregate root

31. Aggregate
• a group of related entities and value objects
• useful when de ning transaction, distribution and
concurrency boundaries
• designate one entity as the aggregate root
• allow external references to only the aggregate root

32. Aggregate
• a group of related entities and value objects
• useful when de ning transaction, distribution and
concurrency boundaries
• designate one entity as the aggregate root
• allow external references to only the aggregate root
• delegate persistence of an aggregate root to a repository

33. Domain Event
1. http://martinfowler.com/eaaDev/EventSourcing.html

34. Domain Event
• something important that happens within the domain that
may lead to a state change in a domain object
1. http://martinfowler.com/eaaDev/EventSourcing.html

35. Domain Event
• something important that happens within the domain that
may lead to a state change in a domain object
• current state can be computed by looking at all currently
known domain events (a.k.a. event sourcing[1])
1. http://martinfowler.com/eaaDev/EventSourcing.html

36. Domain Event
• something important that happens within the domain that
may lead to a state change in a domain object
• current state can be computed by looking at all currently
known domain events (a.k.a. event sourcing[1])
• domain events can trigger other domain events (e.g. three
strikes triggers an out)
1. http://martinfowler.com/eaaDev/EventSourcing.html

37. Supple Design

38. Closure of Operations

39. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object

40. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object

41. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object
• example: 2 + 3 = 5

42. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object
• example: 2 + 3 = 5
• “2” is a value object of type number

43. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object
• example: 2 + 3 = 5
• “2” is a value object of type number
• number has an add method

44. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object
• example: 2 + 3 = 5
• “2” is a value object of type number
• number has an add method
• add method accepts an argument of type number

45. Closure of Operations
• have a method on a value object that returns an instance
of the same type of value object
• any method arguments should also be the same type as
the value object
• example: 2 + 3 = 5
• “2” is a value object of type number
• number has an add method
• add method accepts an argument of type number
• add method returns a number

46. Other Techniques
• intention-revealing interfaces
• side-effect free functions
• assertions

47. Strategic Design

48. Context Map

49. Context Map
• draw a context map of the current bounded contexts

50. Context Map
• draw a context map of the current bounded contexts
• map what actually exists—not what you wish existed!

51. Context Map
• draw a context map of the current bounded contexts
• map what actually exists—not what you wish existed!
• identify relationships between contexts

52. Relationship Patterns
customer/ anticorruption
partnership supplier layer
shared kernel big ball of separate ways
mud
open host conformist published
service language

53. Distillation

54. Multiple Models

55. Multiple Models
• there are always multiple models

56. Multiple Models
• there are always multiple models
• a model my represent:

57. Multiple Models
• there are always multiple models
• a model my represent:
• your core domain

58. Multiple Models
• there are always multiple models
• a model my represent:
• your core domain
• a supporting domain

59. Multiple Models
• there are always multiple models
• a model my represent:
• your core domain
• a supporting domain
• a generic subdomain

60. Multiple Models
• there are always multiple models
• a model my represent:
• your core domain
• a supporting domain
• a generic subdomain
• focus your modeling efforts on the core domain

61. Identifying the Core Domain
Ask organizational leaders and domain experts:
• What keeps you awake at night?
• What makes your system worth writing?
• Why not buy it off the shelf?
• Why not outsource it?

62. Don’t settle on not having
access to a domain expert!

63. Thank You
@BradleyHolt
http://bradley-holt.com
http://joind.in/4003
Copyright © 2011 Bradley Holt. All rights reserved.