Domain Driven Analysis and Design
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Short introduction to Domain Driven analysis and design (DDD)
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Domain Driven Analysis and Design
- 1. Domain Driven Design Analysis and Design Jeppe Cramon - @jeppec Cloud Create ApS
- 2. @jeppec "I consider 'getting the boundaries right' the single design decision with the most significant impact over the entire life of a software project." @ziobrando
- 3. @jeppec 3
- 4. @jeppec This highly depends on • How likely are things to change • And what parts that change together
- 6. @jeppec Result is often fragmented domain logic Focus on Nouns (Entities) and retrofit Verbs later
- 8. @jeppec If we primarily model around nouns/entities we can easily violate the Single Responsibility Principle Where a change to requirements is likely to require changes to multiple entity classes
- 9. @jeppec Business introduces new rule Product price depends on Customer Status
- 12. @jeppec Most applications are built with CRUD as the main paradigm Intention gets lost
- 13. @jeppec We need to shift focus from pure data towards intent and process automation This means a change from CRUD style application design, where the process was implicit and stored in the minds of the users First I need to enter the employee in this screen Then I need to press a button in the user system so they’re properly created And the I need to add their access card to this screen and press Activate
- 14. @jeppec Task-based/Inductive UI • Traditional CRUD UI is what I would call a WHAT UI • Task based UI’s focuses on HOW the user wants to use the application • Guides users through the work process • The UI becomes an intrinsic part of the design • The UI design directly affects our commands and thereby our transactional boundaries
- 15. @jeppec We need to capture User Intent at the UI CRUD style Task based style Intent
- 16. @jeppec Capturing intent in the form of a Command A Command is prescriptive of what should happen, and its primary goal is to capture USER INTENT A Command supports a single usecase and targets a single business object within a single Transaction Commands always carry a name in its imperative form: • AcceptOrder • ShipOrder • CancelOrder • ReimburseCustomer • Etc. “A command describes a Task that you want someone else to carry out for you and where the recipient can choose to reject the Command”
- 17. @jeppec Example public class OrderService { public void handle(AcceptOrder cmd) { orderRepository.add(new Order(cmd.orderId, cmd.orderLines)); … }
- 18. @jeppec instead of focusing on Nouns!
- 19. @jeppec When discussing use cases with Business Experts
- 20. @jeppec and what fields that are separate
- 21. @jeppec
- 23. @jeppec But don’t name the piles before you know what they are This avoids cognitive bias!
- 24. @jeppec Give the piles made up names, such as colors
- 25. @jeppec What are the these problem domain piles?
- 26. @jeppec Business Capability alignment “The advantage of business capabilities is their remarkable level of stability. If we take a typical insurance organisation, it will likely have sales, marketing, policy administration, claims management, risk assessment, billing, payments, customer service, human resource management, rate management, document management, channel management, commissions management, compliance, IT support and human task management capabilities. In fact, any insurance organisation will very likely have many of these capabilities.” See http://bill-poole.blogspot.dk/2008/07/business- capabilities.html
- 27. @jeppec Business – IT alignment • We want the Business and IT to speak the same Ubiquitous language • Want want our architecture to be aligned with the business capabilities • Because these capabilities are stable
- 28. @jeppec Many perspectives on data Online Retail System Product Unit Price Promotional Price Promotion End Date Stock Keeping Unit (SKU) Quantity On Hand (QOH) Location Code Price Quantity Ordered Name The lifecycle of the data is VERY important! Customer Pricing Inventory Sales Management Reporting
- 29. @jeppec Smaller models & clear data ownership Retail System Pricing Product ProductID Unit Price Promotional Price … Pricing Inventory Product ProductID SKU QOH Location Code … Inventory Sales Product ProductID Name Description Quantity Ordered … Sales Shared Entity identity DDD: Bounded Context Business Capability DDD: Aggregate
- 30. @jeppec Aggregates Invoice InvoiceLine * Account * What: • Cluster coherent Entities and Value Objects, with complex associations into Aggregates with well defined boundaries. • Choose one entity to be root and control access to objects inside the boundary through the root. Motivation: Control invariants and consistency through the aggregate root. Ensuring consistency & transactional boundaries for Distributed scenarios! Root * *
- 31. @jeppec Entities Motivators: Objects are defined by identity and NOT by their attributes. May have lifecycle, can change form by time and context (A Person that becomes a father, who becomes a grand father, etc.) Focus is on Who and not on what! Customer - ID/Social Security Number : Number
- 32. @jeppec Value Objects Customer - ID/Social Security Number : Number Address - street : String - zipCode : String 1 Motivators: Objects which Measures, Quantifies or Describes a thing in the domain. They’re immutable and defined by their attributes (not by their identity) and doesn’t have a lifecycle. Focus is on What and not on who!
- 33. @jeppec Aggregates refer to each other by ID they NEVER use memory pointers, join tables or remote calls
- 34. @jeppec Bounded Contexts and Aggregates Sales Product Customer customerId … Order orderId customerId … OrderLine orderId productId quantity timestamp priceId ProductCategory productCategoryId … Pricing Product productId productCategoryId name tag ... Product-Price priceId productId normalPrice discountPeriods …
- 35. @jeppec For more see Blog: https://cramonblog.wordpress.com/ Homepage: http://cloudcreate.dk/ Twitter: @jeppec