Greg Young's presentation discusses modeling domain state transitions and separating commands and queries. It addresses using explicit state representation, storing events, and asynchronous context mapping between bounded contexts. Diagrams show evolving architectures from directly coupled components to eventually consistent designs with denormalized data stores and anti-corruption layers. Key points are that getters and setters are anti-patterns; domains should model state transitions; most queries can tolerate eventual consistency; and the client view differs from the domain model.

1. Unleash Your Domain Greg Young

2. Agenda The Issues The Breakthroughs Explicit State Representation Event Storage Command Query Separation Asynchronous Context Mapping Summary Questions

8. State transitions are an important part of our problem space and should be modeled within our domain.

10. Line Items (n) Purchase Order Shipping Information

12. Purchase Order AddItemCommand AddItemCommand AddItemCommand ChangeAddressCommand

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20. Data Storage Domain Object Domain Object Application Services Remote Facade Request DTO DTO returned Send up DTO Status returned Client

21. Request DTO DTO returned DTO Sent Ack/Nak Response Send DTO Back to Server Show DTO on Screen User Interacts With DTO

24. Data Storage Domain Object Domain Object Thin Read Layer (Direct to DTO) Remote Facade Application Services Remote Facade Request DTO DTO returned Message Sent Ack/Nak Response Client

25. Data Storage Write (Command) Read (Query) Domain Object Domain Object Thin Read Layer (Direct to DTO) Remote Facade Application Services Remote Facade Request DTO DTO returned Message Sent Ack/Nak Response Client

26. A single model cannot be appropriate for reporting, searching, and transactional behaviors…

29. The model that a client needs the data in a distributed system is screen based and different than the domain model.

31. Most queries can operate with relaxed consistency…

32. Data Storage Data Storage Denormalizer ------------------- Anti Corruption Pipeline Domain Object Domain Object Application Services Thin Read Layer (Direct to DTO) Remote Facade Remote Facade Client

34. Getters and Setters are a domain anti-pattern.

38. Most Bounded Contexts can interact with relaxed consistency.

40. Using relaxed consistency allows us to increase our scalability and availability!

41. “Man acts as though he were the shaper and master of language, while in fact it is language that is the master of man.”

42. State transitions are an important part of our problem space and should be modeled within our domain.

43. Getters and Setters are a domain smell.

44. Most Bounded Contexts can interact with relaxed consistency.

45. A single model cannot be appropriate for reporting, searching, and transactional behaviors…

46. Questions