Agile development is getting every year more popular around the world while a less known methodology is the Domain Driven Design (DDD) which defines a few rules to be followed to empower the agile team to raise communication effectiveness. Agile methods and DDD are perfectly matching and used together can solve many problems we are all too sadly used to.

1. Agile development and Domain Driven Design
Jacopo Romei
http://www.sviluppoagile.it/

2. Ego sliding
 Jacopo Romei
 PHP since 1999
 IT CEO in the past
 Freelance agile coach
 http://www.sviluppoagile.it/
Jacopo Romei, http://www.sviluppoagile.it/

3. Agile development
A family of empirical methodologies
Jacopo Romei, http://www.sviluppoagile.it/

4. Agile Manifesto
 Individuals over tools
 Working software over documentation
 Customer collaboration over contract deals
 Accept change over following plans
Jacopo Romei, http://www.sviluppoagile.it/

5. Domain
What does inspire our solutions?
Jacopo Romei, http://www.sviluppoagile.it/

6. Driven
Where do we find our solutions?
Jacopo Romei, http://www.sviluppoagile.it/

7. Design
What does provide us with solutions?
Jacopo Romei, http://www.sviluppoagile.it/

8. Design vs. Process
 Design principles
 Messy reality
 DDD is a way to cope with the mess
 Agile Dev is a way to cope with the mess
Jacopo Romei, http://www.sviluppoagile.it/

9. Manouvrability
Agility means manouvrability
Jacopo Romei, http://www.sviluppoagile.it/

10. Shared values
 Courage
 Respect
Jacopo Romei, http://www.sviluppoagile.it/

11. Shared values
 Courage  Simplicity is the art of
maximizing the amount
 Respect
of work not done
 Simplicity
Jacopo Romei, http://www.sviluppoagile.it/

12. Shared values
 Courage
 Respect
 Simplicity
 Communication
 Feedback
Jacopo Romei, http://www.sviluppoagile.it/

13. Shared values
 Courage  Who
 Respect  Which
 Simplicity  How
 Why
 Communication
 Feedback
Jacopo Romei, http://www.sviluppoagile.it/

14. XP and good design
 Refactoring tries to avoid overengineering
 Refactoring can develop underengineering
 XP works best with good designers
 DDD helps developers being good designers
Jacopo Romei, http://www.sviluppoagile.it/

15. Don't ossify, please
Supple, knowledge­rich design
Jacopo Romei, http://www.sviluppoagile.it/

16. Orthogonality
•Orthogonality is a system design property facilitating
feasibility and compactness of complex designs.
• Orthogonality guarantees that modifying the technical
effect produced by a component of a system neither
creates nor propagates side effects to other components of
the system.
•Emergent behavior of a system should be controlled strictly
by formal definitions of its logic and not by side effects
resulting from poor integratio
•Orthogonality reduces testing and development time
Jacopo Romei, http://www.sviluppoagile.it/

17. Shared required practices
 Iterative and incremental development
 Close relationship with domain experts
 Refactoring
Jacopo Romei, http://www.sviluppoagile.it/

18. UX & Agile
Methodology to write user stories
Jacopo Romei, http://www.sviluppoagile.it/

19. DDD & Agile
Methodology to (let emerge) design
Jacopo Romei, http://www.sviluppoagile.it/

20. Ubiquitous language
One jargon to rule them all
Jacopo Romei, http://www.sviluppoagile.it/

21. Ubiquitous language
 Model as backbone of language in
 Code
 Diagrams
 Writings
 Speech
Jacopo Romei, http://www.sviluppoagile.it/

22. Ubiquitous language
 Refactor
 Classes
 Methods
 Modules
 Reflect
 Real world entities
 Confusion resolution in conversations
 Changes in language as changes in model
Jacopo Romei, http://www.sviluppoagile.it/

23. Example
Jacopo Romei, http://www.sviluppoagile.it/

24. Short example
 “If we give the Routing Service an origin,
destination and arrival time, it can look up the
stops the cargo will have to make and well... stick
them in the database”
 “The origin, destination and so on... it all feeds into
Routing Service and we get back an Itinerary
that has everything we need it”
 “A Routing Service finds an Itinerary that satisfies
a Route Specification”
Jacopo Romei, http://www.sviluppoagile.it/

25. Documentation
Agile methodologies value working software over
comprehensive documentation
Jacopo Romei, http://www.sviluppoagile.it/

26. UML is not enough
UML doesn't convoy the concepts behind a model
UML doesn't convoy what objects are meant to do
Jacopo Romei, http://www.sviluppoagile.it/

27. Ubiquitous documentation
UML provides some documentation
Code provides some documentation
Ubiquitous language provides some documentation
Jacopo Romei, http://www.sviluppoagile.it/

28. Hands-on modelers
Everyone who writes code must feel responsible for
the model.
Jacopo Romei, http://www.sviluppoagile.it/

29. Hands-on modelers
Everyone who writes code must feel responsible for
the model.
Everyone contributing to the model must touch the
code.
Jacopo Romei, http://www.sviluppoagile.it/

30. Hands-on modelers
Everyone who writes code must feel responsible for
the model.
Everyone contributing to the model must touch the
code.
That's a DDD team. That's an agile team.
Jacopo Romei, http://www.sviluppoagile.it/

31. Modeling paradigm
Object oriented programming is good to model the
way we think about things. OO community
developed lots of critically meaningful concepts.
PHP community: WAKE UP!
Jacopo Romei, http://www.sviluppoagile.it/

32. Deadly divide
 Model can be absent (brrr...)
 Model can be overdesigned
 Model can be detached from the domain
 Suspect correctness
 Hard to maintain
 Difficult to understand
Jacopo Romei, http://www.sviluppoagile.it/

33. Reflection
Software must reflect domain model
Jacopo Romei, http://www.sviluppoagile.it/

34. Ubiquity
Software must reflect ubiquitous language
Jacopo Romei, http://www.sviluppoagile.it/

35. Building blocks
 Layered architecture
 Services
 Entities
 Value Objects
 Factories
 Aggregates
 Repositories
Jacopo Romei, http://www.sviluppoagile.it/

36. Layers
 User interface
 Smart UI vs. Model Driven Design
Jacopo Romei, http://www.sviluppoagile.it/

37. Layers
 User interface
 Smart UI vs. Model Driven Design
 Application
 a.k.a. Controller
Jacopo Romei, http://www.sviluppoagile.it/

38. Layers
 User interface
 Smart UI vs. Model Driven Design
 Application
 a.k.a. Controller
 Domain/Model layer
Jacopo Romei, http://www.sviluppoagile.it/

39. Layers
 User interface
 Smart UI vs. Model Driven Design
 Application
 a.k.a. Controller
 Domain/Model layer
 Infrastructure
Jacopo Romei, http://www.sviluppoagile.it/

40. Frameworks
Free choice, but domain layer must be preserved.
Jacopo Romei, http://www.sviluppoagile.it/

41. The end, the beginning
No one said agile was easy.
No one said it was a standalone concept.
Jacopo Romei, http://www.sviluppoagile.it/

42. What's next
Agile Day 2009
Jacopo Romei, http://www.sviluppoagile.it/

43. Jacopo Romei
jacopo [at] sviluppoagile.it
skype: jacoporomei
www.sviluppoagile.it
Jacopo Romei, http://www.sviluppoagile.it/