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

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

3.
do·maindōˈmān 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

16.
Building Blocks

17.
Entity

18.
Entity• de ned by a thread of continuity and identity

19.
Entity• de ned by a thread of continuity and identity• only responsibilities should be around identity and life cycle

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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

21.
Value Object

22.
Value Object• de ned by its encapsulated attributes

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

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

25.
De ning an object as an entity or avalue object is context-dependent.

26.
Aggregate

27.
Aggregate• a group of related entities and value objects

28.
Aggregate• a group of related entities and value objects• useful when de ning transaction, distribution and concurrency boundaries

29.
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

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• allow external references to only 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• delegate persistence of an aggregate root to a repository

32.
Domain Event 1. http://martinfowler.com/eaaDev/EventSourcing.html

33.
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

34.
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

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])• domain events can trigger other domain events (e.g. three strikes triggers an out) 1. http://martinfowler.com/eaaDev/EventSourcing.html

36.
Supple Design

37.
Closure of Operations

38.
Closure of Operations• have a method on a value object that returns an instance of the same type of value object

39.
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

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• example: 2 + 3 = 5

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 • “2” is a value object of type number

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 • number has an add method

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 • add method accepts an argument of type number

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 • add method returns a number

45.
Other Techniques• intention-revealing interfaces• side-effect free functions• assertions

46.
Strategic Design

47.
Context Map

48.
Context Map• draw a context map of the current bounded contexts

49.
Context Map• draw a context map of the current bounded contexts• map what actually exists—not what you wish existed!

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

51.
Relationship Patterns customer/ anticorruption partnership supplier layershared kernel big ball of separate ways mud open host conformist published service language

52.
Distillation

53.
Multiple Models

54.
Multiple Models• there are always multiple models

55.
Multiple Models• there are always multiple models• a model my represent:

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

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

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

59.
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

60.
Identifying the Core DomainAsk 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?

61.
Don’t settle on not havingaccess to a domain expert!

62.
Thank You @BradleyHolt http://bradley-holt.com http://joind.in/4003Copyright © 2011 Bradley Holt. All rights reserved.