Domain-Driven Data at TechBash

8896271ee9d6f46d4b1783c9566cb645?s=47 Bradley Holt
September 29, 2016

Domain-Driven Data at TechBash

There are many types of databases and data analysis tools from which to choose today. Should you use a relational database? How about a key-value store? Maybe a document database? Or is a graph database the right fit for your project? What about polyglot persistence? Help! Applying principles from Domain-Driven Design such as strategic design and bounded contexts, this presentation will help you choose and apply the right data layer for your application's model or models. We will explore traditional relational databases, graph databases, document databases, key/value stores, polyglot persistence, CQRS, event sourcing, and data layers for microservices.


Bradley Holt

September 29, 2016


  1. TechBash Bradley Holt, Developer Advocate Thursday, September 29, 2016 Domain-Driven

    Data @BradleyHolt
  2. @BradleyHolt

  3. None
  4. None
  5. None
  6. Big Data Get it?

  7. IBM Cloud Data Services Open for Data A comprehensive por.olio

    of open source data services
  8. A Brief History of Data

  9. The Relational Database @BradleyHolt order *order_id customer_id date customer line_item

    *customer_id email_address name *order_id *item_id price quantity
  10. ACID Guarantees Relational databases guarantee atomicity, consistency, isolation and durability

  11. Big Iron The ACID guarantees provided by relational databases were

    (and often still are) critical for systems of record
  12. The World Wide Web The introduction of the Web brought

    a whole new type of application with different constraints than systems of record @BradleyHolt
  13. Mobile Apps The introduction of mobile apps added to the

    growing number of systems of engagement
  14. Changing Constraints

  15. Always On

  16. Big Data

  17. The CAP Theorem @BradleyHolt Partition Tolerance Availability Consistency Consistency Availability

    Partition Tolerance
  18. Horizontal Scaling Horizontal scaling is scaling through the addition of

    commodity hardware
  19. Eventual Consistency Given no new updates, each node in a

    distributed system will eventually have a consistent view of the data
  20. Enter "Not only SQL" (NoSQL)

  21. @BradleyHolt key-value graph document …more

  22. @BradleyHolt

  23. Key-Value Stores Opaque data accessed through unique keys

  24. Document Databases A variation on key-value stores with strictly defined

    values (e.g. JSON objects)
  25. Graph Databases Nodes and properties of nodes connected via edges

  26. Domain-Driven Design (DDD)

  27. @BradleyHolt

  28. Domain-Driven Design A collaboration between domain experts and software practitioners

  29. Complexity is in the Domain Complexity is in the domain,

    not in the technology
  30. Models as Tools Models are tools used to solve problems

    within the domain
  31. The Map is not the Territory Don't confuse models with

    reality itself
  32. Building Blocks of DDD and the Life Cycle of a

    Domain Object
  33. Entities Entities are defined by their identity

  34. Value Objects Value objects encode attributes that describe things

  35. Aggregates Aggregates group related entities to minimize complexity

  36. Repositories A repository provides the illusion of an in-memory data

  37. Domain Layer Order Aggregate @BradleyHolt «interface» OrderRepository + insertOrder(order:Order) +

    updateOrder(order:Order) + findOrderById(id:int) : Order + recentOrders([limit:int]) : Order[0..*] Customer … Infrastructure Layer LineItem … Order - id : int - customer : Customer - date : Date - lineItems : LineItem[1..*] + total() : Money InMemoryOrderRepository + insertOrder(order:Order) + updateOrder(order:Order) + findOrderById(id:int) : Order + recentOrders(limit:int) : Order[0..*] RelationalMapperOrderRepository + insertOrder(order:Order) + updateOrder(order:Order) + findOrderById(id:int) : Order + recentOrders(limit:int) : Order[0..*]
  38. Choosing the Right Data Layer

  39. Data Store A repository cannot abstract the constraints of your

    data store
  40. Object-Relational Impedance Mismatch Object-oriented programming and relational databases use different

  41. Eric Evans on NoSQL "This is the world of NoSQL

    to me, that we can choose a tool that fits well with the problem we're trying to solve." –Eric Evans (author of Domain-Driven Design) @BradleyHolt
  42. Strategic Design

  43. Bounded Context Bounded contexts allow different domain models to be

    used within different contexts
  44. One Data Layer Per Bounded Context Each bounded context should

    have its own data layer, and should not directly access a data layer belonging to another bounded context
  45. Data Systems A data layer may be a database, or

    it can be a data system consisting of multiple databases
  46. Microservices as Bounded Context Represent each bounded context as a

    microservice or a cluster of microservices
  47. @BradleyHolt Catalog Document Database Key/Value Store Graph Database Full Text

    Search Shopping Cart Document Database Key/Value Store Orders Relational Database Big Data Analytics
  48. Alternative Architectures

  49. Command Query Responsibility Segregation (CQRS) Rather than update an entity

    in place, CQRS provides separate read and write models
  50. Domain Layer @BradleyHolt Read Model «interface» OrderQueryHandler + findOrderById(id:int) :

    OrderDetails + recentOrders([limit:int]) : OrderSummary[0..*] Write Model OrderDetails + getId() : int + getCustomer() : Customer + getDate() : Date + getLineItems() : LineItem[1..*] + getTotal() : Money «interface» OrderCommandHandler + handle(command:CreateOrder) + handle(command:AddLineItem) CreateOrder - customer : Customer - date : Date - lineItems : LineItem[1..*] OrderSummary + getId() : int + getDate() : Date + getTotal() : Money AddLineItem - orderId : int - lineItem : LineItem
  51. Event Sourcing The current application state is computed from a

    sequence of events
  52. IBM Cloud Data Services Open for Data A comprehensive por.olio

    of open source data services
  53. None
  54. Image Credits §  Open for Data Dome (outside) by Bradley

    Holt §  Open for Data Dome (inside) by Bradley Holt §  Brent Spiner (Data from Star Trek: The Next Generation) with Zoltar from Big by Bradley Holt, on Twitter <> §  database 2 by Tim Morgan, on Flickr <> §  Hard Disk by Jeff Kubina, on Flickr <> §  IBM 360 Announcement center by Robert Nix, on Flickr <> §  Dialing Up Web History by Mike Licht, on Flickr <> §  Instagram and other Social Media Apps by Jason Howie, on Flickr <> §  Dynamo, un siècle de lumière et de mouvement dans l'art, 1913 – 2013 - Galeries nationales du Grand Palais - Paris - 10 avril au 22 juillet 2013 by Yann Caradec, on Flickr < §  World travel and communications recorded on Twitter by Eric Fischer, on Flickr <> §  Server grill with blue light by David Precious, on Flickr <> §  Spider Web by Alden Chadwick, on Flickr <> §  database by Tim Morgan, on Flickr <> §  Keys for the Stanley Hotel by Mike Silva, on Flickr <> §  paper by malik, on Flickr <> §  Edinburgh Road Network analysis by Steven Kay, on Flickr <> @BradleyHolt
  55. Image Credits (cont'd) §  IMG_2619 by Jason Pelletier, on Flickr

    <> §  Sounds_of_Complexity11.jpg by Enzo Varriale, on Flickr <> §  model by MaZzuk, on Flickr <> §  taking the subway to find the rents by Eli Duke, on Flickr <> §  DSC_3407 by Mad House Photography, on Flickr <> §  red numbers by DaveBleasdale, on Flickr <> §  Social graph by Dmitry Grigoriev, on Flickr <> §  Catalog. by Adam Mayer, on Flickr <> §  Lina Bo Bardi, SESC Pompéia by paulisson miura, on Flickr <> §  Financial District Classical Building Reflection Distortion, San Francisco, California, USA by Wonderlane, on Flickr <> §  Eric Evans by Oliver Gierke, on Flickr <> §  rectangles by Dean Hochman, on Flickr <> §  Hexagons by Henry Burrows, on Flickr <> §  Rooted by Anna Levinzon, on Flickr <> §  Rainforest Biome by BMiz, on Flickr <> §  rectangles-10 by Karen Cropper, on Flickr <> §  Rusty Chain by veggiefrog, on Flickr <> @BradleyHolt
  56. Thank You @BradleyHolt