Getting modules right with Domain-driven Design

Domain-driven Design helps teams achieve a better alignment between the business and the technical architecture in order to design applications that have highly expressive and maintainable domain models. This talk aims at giving you an overview of Domain-driven Design and how the ideas behind it help you to create better modular applications.

We will talk about aspects from strategic Domain-driven Design such as Bounded Contexts and Subdomains, in addition to that the talk will explain the most important patterns from the tactical part of Domain-driven Design (Aggregate, Entity, Value Object). Finally you will learn about methods that help you in getting a better understanding about the domain you are working in.

Transcript

1. Getting Modules
   Right
   MICHAEL PLÖD
   FELLOW
   with Domain Driven Design
   

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2. Get my DDD book
   cheaper
   Book Voucher: 7.99 instead of (min) 9.99
   http://leanpub.com/ddd-by-example/c/speakerdeck
   

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3. Michael Plöd
   Fellow at INNOQ
   Follow me on Twitter under @bitboss
   Current consulting topics:
   • Domain-Driven Design
   • Team Topologies
   • Transformation from IT Delivery to digital product orgs
   Regular speaker at (inter-)national conferences and author of a
   book + various articles
   

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4. Separation of Concerns
   is the division of complex
   systems according to
   responsibility
   

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5. Modularity
   is a specialization of SoC and about
   information hiding
   loose coupling
   high cohesion
   

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6. Domain Driven
   Design
   has great modularization
   concepts (Bounded
   Context, Aggregate) and an
   iterative approach for the
   identi ication of modules
   

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7. Bounded
   Context
   Bounded
   Context
   Bounded
   Context
   Module Granularity in DDD
   

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8. Bounded
   Context
   Bounded
   Context
   Bounded
   Context
   Module Granularity in DDD
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   Aggregate
   

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9. Bounded
   Context
   Bounded
   Context
   Bounded
   Context
   Let’s start with Bounded Contexts
   

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10. https://github.com/ddd-crew/ddd-starter-modelling-process
    

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11. https://github.com/ddd-crew/ddd-starter-modelling-process
    

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12. https://github.com/ddd-crew/ddd-starter-modelling-process
    

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13. https://github.com/ddd-crew/ddd-starter-modelling-process
    

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14. „It is not the domain
    experts knowledge that
    goes into production, it is
    the assumption of the
    developers that goes into
    production”
    11
    Alberto Brandolini
    Inventor of EventStorming
    

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15. A B
    C
    „Gut, dass wir alle einer Meinung sind!“
    Inspiriert durch Jeff Patton & Luke Barren
    „good that we all share the same
    opinion“
    

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16. for doing Domain Driven Design
    Domain expert knowledge is essential
    

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17. we need direct collaboration
    

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19. How the business names things
    TV
    Window
    Chair
    Trolley
    Painting
    Desk
    

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20. How the business names things
    TV
    Window
    Chair
    Trolley
    Painting
    Desk
    What we see in code
    TransparencyFactory
    RollableStuffContainer
    EntertainmentProviderSingleton
    DecoratorImpl
    RestProvider
    WorkEnablementDevice
    

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21. DOMAIN MODEL
    Domain Experts
    Developers
    Ubiquitous Language
    Conversations
    Code
    Drawings Documentation
    

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22. Event Storming
    is a direct collaboration workshop for various stakeholders of a piece of software
    

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23. Chaotic Exploration
    A Domain Event is the main concept of EventStorming. It is an event
    that is relevant for the domain experts and contextual for the domain
    that is being explored. A Domain Event is a verb at the past tense. The
    of icial EventStorming colour is orange.
    

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24. Enforcing the timeline
    In a second step we sort those events along a timeline. This will ignite
    quite a few discussions and may take some time.
    

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25. Pivotal Events & Swimlanes
    Mark those events that are very important. Those are your pivotal
    events. You may also highlight parallel streams of activity with
    swimlanes.
    

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26. Quiz: which of these events are pivotal?
    

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27. Quiz: which of these events are pivotal?
    

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28. 23
    https://github.com/ddd-crew/ddd-starter-modelling-process
    

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29. Text...
    Shape... Color... Size...
    There are many choices to group domain concepts
    24
    Output quantity
    

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30. Boundaries between Pivotal Events
    Heuristic: A pivotal event will probably sit on a boundary of a module
    

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31. Mind the swimlanes
    Heuristic: Swimlanes can help you in identifying further cohesion criteria
    

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32. Bounded Context
    A Bounded Context is a boundary for a
    model expressed in a consistent language
    tailored around a speci ic purpose
    

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33. A Bounded
    Context is a
    boundary for a
    model
    expressed in a
    consistent
    language
    tailored around
    a speci ic
    purpose
    Boundary
    Learning and
    mastering domain
    complexity
    Conducting
    experiments /
    Learning
    Delivering high
    value software
    

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34. A Bounded
    Context is a
    boundary for a
    model
    expressed in a
    consistent
    language
    tailored around
    a speci ic
    purpose
    Boundary for a model
    Business Rules
    Decisions
    Policies
    

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35. A Bounded
    Context is a
    boundary for a
    model
    expressed in a
    consistent
    language
    tailored around
    a speci ic
    purpose
    Language
    Terminology
    De initions
    Meaning
    

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36. A fruit or a vegetable?
    What is a tomato?
    

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37. A fruit or a vegetable?
    What is a tomato?
    

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38. Fruit
    Botanics
    A fruit or a vegetable?
    What is a tomato?
    

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39. Fruit
    Botanics
    Vegetable
    Cooking
    A fruit or a vegetable?
    What is a tomato?
    

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40. Fruit
    Botanics
    Vegetable
    Cooking
    US
    Customs
    A fruit or a vegetable?
    What is a tomato?
    

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41. Fruit
    Botanics
    Vegetable
    Cooking
    US
    Customs
    25 Min
    Time Management
    A fruit or a vegetable?
    What is a tomato?
    

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42. Fruit
    Botanics
    Vegetable
    Cooking
    US
    Customs
    25 Min
    Time Management
    Feedback
    Theater
    A fruit or a vegetable?
    What is a tomato?
    

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43. A Bounded
    Context is a
    boundary for a
    model
    expressed in a
    consistent
    language
    tailored around
    a speci ic
    purpose
    Purpose
    Language
    Rules
    Speci ic Model
    

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44. Botanics-US Customs-Cooking-Time management-
    Feedback
    Tomato
    It aims at speci ic models tied to a speci ic purpose
    The Bounded Context is not about the
    

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45. Some IT conference
    Registration of visitors
    Lunch planning
    Printing of badges
    Room planning
    Selling tickets
    Handling of payments
    

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46. YOU at some IT conference
    Registration of visitors
    Lunch planning
    Printing of badges
    Room planning Selling tickets
    Handling of payments
    

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47. You can group concerns
    Lunch planning
    Room planning
    Event
    Management
    Printing of badges
    Badges
    Registration of visitors
    Selling tickets
    Handling of payments
    Ticket Sales
    

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48. Don’t
    Repeat
    Yourself
    

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49. YOU at some IT conference
    Registration of visitors
    Lunch planning
    Printing of badges
    Room planning Selling tickets
    Handling of payments
    

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50. Bounded Context
    A Bounded Context is a boundary for a
    model expressed in a consistent language
    tailored around a speci ic purpose
    

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51. This has no purpose at all and the
    language is also not speci ic here
    

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52. Maybe those are interesting bounded context candidates?
    Event
    Management
    Badges
    Ticket
    Sales
    

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53. Look for terminology
    Application
    Form
    Scoring
    Rule Cluster
    Documents
    Real Estate
    Veri ication
    Income
    Veri ication
    Rejection
    Reference
    Properties
    Rejection
    Scoring
    Rule Cluster
    Credit
    Decision
    Template
    Credit
    Decision
    Hierarchy
    Contract
    Proposal
    Contract
    Welcome
    Letter
    Repayment
    Plan
    Decision
    

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54. 44
    https://github.com/ddd-crew/ddd-starter-modelling-process
    

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55. 45
    Domain Message Flow Modelling
    A Domain Message Flow Diagram is a simple visualization showing the low of messages
    (commands, events, queries) between actors, bounded contexts, and systems, for a single scenario.
    Source: https://github.com/ddd-crew/domain-message- low-modelling
    

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57. 47
    https://github.com/ddd-crew/ddd-starter-modelling-process
    

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58. 47
    https://github.com/ddd-crew/ddd-starter-modelling-process
    

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59. 48
    Bounded Context Design Canvas
    The canvas guides you through the process of designing a bounded context by requiring you to
    consider and make choices about the key elements of its design, from naming to responsibilities, to
    its public interface and dependencies.
    Source: https://github.com/ddd-crew/bounded-context-canvas
    

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61. COHESION
    Think about
    

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66. Bounded
    Context
    Bounded
    Context
    Bounded
    Context
    Let’s dig into the Bounded Contexts
    

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67. Bounded
    Context
    Bounded
    Context
    Bounded
    Context
    Let’s dig into the Bounded Contexts
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    Aggregate
    

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68. 56
    https://github.com/ddd-crew/ddd-starter-modelling-process
    

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69. Everything from here on is
    inside a Bounded Context
    We are now talking about more ine grained modules
    

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70. Aggregates
    (Internal)
    Building Blocks
    Entities
    Value Objects
    Factories
    Services
    Repositories
    TACTICAL
    DESIGN
    helps us with regards to
    evolvability of
    microservices
    

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71. Entities
    Entities represent the core
    business objects of a
    bounded context’s model
    Each Entity has a
    constant identity
    Each Entity has its own
    lifecycle
    Customer
    Credit
    Application
    Shipment
    

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72. Value Objects
    Value Objects derive their
    identity from their values
    Value Objects do not have
    their own lifecycle, they
    inherit it from Entities
    that are referencing them
    You should always
    consider value objects for
    your domain model
    Color
    Monetary
    Amount
    Customer
    

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73. Entity
    Value Value
    

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74. Entity
    Value Value
    Using only Entities and Value
    Objects you will end up with
    big object graphs
    

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75. Entity
    Value Value
    Aggregates group Entities and Value Objects
    

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76. ROOT ROOT
    ROOT
    Value Value
    ROOT
    Each Aggregate has a Root Entity, aka Aggregate Root
    

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77. 
    SelfDisclosure
    
    Address
    
    RedemptionDetail
    
    Loan
    
    LoanApplicationForm
    
    
    CustomerNumber
    
    Customer
    Consider using Value Objects as indirect references
    between Aggregates
    

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78. Aggregate
    Domain
    Concepts
    Aggregates represent higher level business concepts.
    Behavior
    Try moving behavior to Value Objects in the
    Aggregates. The Entities should deal with lifecycle and
    identitiy.
    Invariants
    Aggregates allow us to implement and enforce rules
    and invariants (a incancial situation must have in-
    and outgoings)
    

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79. Hints
    Small
    Prefer small aggregates that usually only contain an
    Entity and some Value Objects.
    Consistency
    Boundaries
    Take a look which parts of your model must be
    updated in an atomically consistent manner
    One TX per
    Aggregate
    Aggregates should be updated in separate
    transactions which leads to eventual consistency
    Reference by
    Identity
    Do not implement direct references to other Root
    Entities. Prefer referencing to Identity Value Objects
    

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80. Design Level EventStorming
    helps you to
    identify and design aggregates
    

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81. Design Level EventStorming
    

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82. Starting point
    

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83. Chaotic Exploration on business rules
    

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84. Which grouping of the rules is the right one?
    

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85. „the key to incremental architecture
    is to build on a framework that can
    accommodate change... that
    framework is the domain.... By
    modeling the domain, you can more
    easily handle changes to the domain“
    Allen Holub
    https:/
    /holub.com
    

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86. These groups
    are great
    candidates for
    aggregates!
    

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87. OOAD usually starts with nouns as class candidates,
    then goes to attributes and then verbs (methods)
    DDD starts with behavior (verbs) and looks then on
    structures
    Mind the difference between this
    approach and the classic object
    oriented analysis and design (OOAD)
    

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89. www.innoq.com
    Thanks!
    Michael Plöd
    Twitter: @bitboss
    LinkedIn: https://www.linkedin.com/in/michael-ploed/
    Get my DDD book at a discount with:
    https:/
    /leanpub.com/ddd-by-example/c/speakerdeck
    (or by scanning the QR code)
    Check out https:/
    /socreatory.com for DDD trainings with me
    (onsite or online as well as in German or English)
    

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