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DDD Basics - Context mapping

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A Context Map will visualize your system: cluttered models, too much or not enough communication, dependencies on other systems are just some of the insights you'll gain if your start using them

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DDD Basics - Context mapping

  1. 1. Stijn Volders @ONE75 http://blog.one75.be
  2. 2. Context Mapping Why a Context Map is essential for the success of your project domaindriven.be – DDD Basics
  3. 3. What • A simple diagram with Bounded Context’s who are involved in your project an your relation with them
  4. 4. Why • Get insight in inter-team communication an their bandwith • Measure to which extent a vision could be shared • Help to decide if DDD is appropriate
  5. 5. It’s all about relations
  6. 6. Relations fall into Patterns • Partnership • Customer/Supplier • Big Ball of Mud • Conformist • Shared Kernel • Separate Ways
  7. 7. All relations have their price
  8. 8. Definition: Partnership When teams in 2 contexts succeed or fail together • Co-ordintad planning of development and joint management of integration • Interdependent features should be scheduled so that they are completed for the same release
  9. 9. Definition: Customer - Supplier • 2 teams in an upstream/downstream relationship • Upstream can succeed interdependently of the downstream team • Downstream priorities factor into upstream planning
  10. 10. Definition: Big Ball of Mud When you have to deal with a big, monolithic (legacy) system • Often with large intermixed models
  11. 11. Definition: Conformist • 2 teams in an upstream/downstream relationship • Upstream has no motivation to provide for the downstream team’s needs • Downstream team doesn’t put effort in translation
  12. 12. Definition: Shared Kernel Sharing a part of the model • Very intimite interdependency • Can leverage or undermine design work • Must be kept small!
  13. 13. Definition: Separate Ways Used to cut loose systems • Integration is always expensive • When there is little to zero interest/benefit in integration
  14. 14. Definition: Anticorruption Layer • Isolating layer to limit impact of changes in an upstream system • Requires little or no modification to the upstream system • Translates in both directions between the 2 models
  15. 15. Definition: Open Host Service When you want to open your system for integration • Protocol that gives access to your system as a set of services • Open for everyone that needs to integrate with your system • New services can be added on request but need to serve a “general” purpose
  16. 16. Definition: Published Language When you want a common language for translation between 2 bounded contexts • Often combined with Open Host Service
  17. 17. Upstream/Downstream
  18. 18. Upstream/Downstream • Not about the direction of the data! • Upstream will influence downstream • Might be technical (code) • But also: schedule, responsiveness to external requests...
  19. 19. Attention! • Map the current situation, not the (desired) future • If it’s a mess, show it. It’ll bring focus to the problems & risks involved in your project.
  20. 20. Let’s try it!
  21. 21. Domain: Amazon
  22. 22. Step 1 • Draw each Context with the name (as known in the UL)
  23. 23. Step 2 • Define which models communicate • Bandwith
  24. 24. Step 3 • Indicate the direction of the relation, if applicable (Upstream/Downstream)
  25. 25. Step 4 • Put the name of the Pattern on the relationship • Partnership • Customer/Supplier • Conformist • Separate Ways • Big Ball of Mud • Shared Kernel
  26. 26. Step 5 • Indicate which BC’s have explicit translation or sharing • Anti Corruption Layer • Open Host/Published Language
  27. 27. Questions? Stijn Volders @ONE75 http://blog.one75.be

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