This document introduces the Distributed Context and Interactions (DCI) architectural pattern. DCI models an application as a network of communicating objects that work together to achieve a common goal through use cases. Unlike class-oriented designs, DCI focuses on objects, their states and behaviors within different contexts. It represents the user's mental model more closely by separating an object's persistent data from its transient roles and behaviors in various use cases. DCI allows flexible and maintainable development by making it easy to add or modify system behaviors without changing the core data model. While tied to specific frameworks, DCI promotes an object-oriented way of thinking that is closer to how people naturally conceptualize a problem domain.

1. DCI – хорошо забытый
старый взгляд на объекты
Anton Chernetskiy
Lev Sivashov
May 1, 2012 www.ExigenServices.com

2. About us
Lev Sivashov Anton Chernetskiy
Developers in Exigen Services

3. What the heck is OOP?
Mixins
Interfaces
Classes
Traits
Prototypes
OOP
Roles
Aspects
Objects

4. Essence of OOP
Networks of communicating objects
work together to achieve
a common goal

5. Class orientation
Static class definitions are not capable of fully
describing dynamic nature of interacting objects

6. Fragmentation instead of
decomposition

8. How
to
understand?

9. Extension
of your
mental model

10. So?

11. So?
• OOP is not a smart programming
tool but a way of thinking

12. So?
• OOP is not a smart programming
tool but a new way of thinking
• Objects are not data structures
with methods but elements of
human mental model

13. So what?

14. Business rules
Software

15. User Programmer
Classes, attributes, met
Object interactions
hods

16. Representing the user's mental model

17. Representing the user's mental model
One-to-one

18. Maintainability
Stable /

19. Introducing DCI

20. Network of communicating objects

21. Use case 1 Use case 2

22. Roles and contexts
At work At home At corporate

23. Data
Context
Interactions

24. Data – what-the-system-is
public class Foo{
public String bar;
public double baz;
}
Very dump objects

25. Context – a use case

26. Interactions
what-the-system-does

27. Object
=
Data + Roles

28. State Behavior

29. State Behavior
Data Context and
Interactions

30. State Behavior
Data Context and
Interactions
User’s
Use cases
mental model

31. State Behavior
Data Context and
Interactions
User’s
Use cases
mental model
Stable Changing

32. In code

33. Implementations
• Scala (traits)
• Ruby, Python (runtime methods injection)
• C++ (templates)
• C# (extension methods)
• Perl
• PHP
• Java (Qi4j)

34. Use cases:

35. Use cases:

36. Use cases:

37. Use cases:

38. Data
public interface Unit {
Property<Integer> health();
Property<String> name();
}

39. Role (attackable)
public interface Attackable {
void receiveDamage(double damageAmount);
}

40. Role implementation (attackable)
class AttackableImpl implements Attackable {
@This
Unit unit;
public void receiveDamage(double damageAmount) {
Double health = unit.health().get();
unit.health().set(health - damageAmount);
}
}

41. Bind implementation to role
@Mixins({AttackableImpl.class})
public interface Attackable {
void receiveDamage(double damageAmount);
}

42. Role (attacker)
public interface Attacker {
void beat(Attackable attackable);
}

43. Role implementation (attacker)
class AttackerImpl implements Attacker {
private final static Integer STRENGTH = 10;
public void beat(Attackable attackable) {
attackable.receiveDamage(STRENGTH);
}
}

44. Context
public class AttackEnemiesContext {
...
Attacker attacker;
List<? extends Attackable> enemies;
public void fight() {
for (Attackable enemy : enemies) {
attacker.beat(enemy);
}
}
}

45. Constructing an object
public interface Worker extends EntityComposite,
Attackable,
Healable,
Builder {
}

46. Initializing unit
EntityBuilder<Worker> builder
= unitOfWork.newEntityBuilder(Worker.class, name);
Unit unit = builder.instanceFor(Unit.class);
unit.health().set(100.0);
unit.name().set(name);
worker = builder.newInstance();

47. Interaction
// Team one
private Warrior warrior;
// Team two
private Worker worker;
private Medic medic;
private Barn barn;

48. barn = worker.buildBarn(); // worker builds barn
new AttackEnemiesContext( // warrior fights everyone
warrior, Arrays.asList(worker, medic, barn)
).fight();
new HealAlliesContext( // doctor heals allies
medic, Arrays.asList(medic, worker)
).healAll();
new RepairBuildingsContext( // worker repairs barn
worker, Arrays.asList(barn)
).repair();

49. But, requirements had changed

50. Use cases:

51. Use cases:

52. Role
public interface Attacker {
void beat(Attackable attackable);
}

53. Object
public interface Worker extends EntityComposite,
Attackable,
Healable,
Builder,
Attacker {
}

54. Old role implementation
class AttackerImpl implements Attacker {
private final static Integer STRENGTH = 10;
public void beat(Attackable attackable) {
attackable.receiveDamage(STRENGTH);
}
}

55. New role implementation
interface AttackerStats {
Property<Integer> strength();
}
class AttackerImpl implements Attacker {
@This
AttackerStats attackerStats;
public void beat(Attackable attackable) {
attackable.receiveDamage(
attackerStats.strength().get()
);
}
}

56. Initializing unit
EntityBuilder<Worker> builder
= unitOfWork.newEntityBuilder(Worker.class, name);
Unit unit = builder.instanceFor(Unit.class);
unit.health().set(100.0);
unit.name().set(name);
AttackerStats attackerStats =
builder.instanceFor(AttackerStats.class);
attackerStats.strength().set(5);
worker = builder.newInstance();

57. new AttackEnemiesContext( // warrior fights everyone
warrior, Arrays.asList(worker, medic, barn)
).fight();
new HealAlliesContext( // doctor heals allies
medic, Arrays.asList(medic, worker)
).healAll();
new AttackEnemiesContext( // worker’s revenge
worker, Arrays.asList(warrior)
).fight();

58. Pros
• Giving system behavior first class status
• Easy to maintain
• Object style of thinking is closer to peoples
mental models rather than class style

59. Cons
• We are strongly tied to Qi4j
• Poor community
• Developer must communicate a lot with
customer.

60. Try it yourself!
https://github.com/Qi4jSample/Qi4jSample
Questions?