Thursday, 29 June 2017

UML - What do those Arrows Mean?

In PlantUML:
@startuml
abstract class Animal
interface Behaviour
interface Prey
Animal <|-- Lion : inheritance
Behaviour <|.. Animal : realization/implementation
Lion *-left- Pride : aggregation
interface Grouping
Grouping <|.. Pride 
Prey o-left- Lion : composition
Water <-down- Lion : uni-directional
Habitat -up- Lion : bi-directional
@enduml
implementation/realization
a dotted line with a closed, unfilled arrow means realization (or implementation). The arrow points to the interface.
inheritance
Inheritance is indicated by a solid line with a closed, unfilled arrowhead pointing at the super class
aggregation
a solid line with an unfilled diamond at the class which contains the other class
composition
a solid line with an filled diamond at the class which uses the other class
bi-directional association
A bi-directional association is indicated by a solid line between the two classes. In the example, the Lion lives in his Habitat, but the Habitat benefits in some way from the Lion as well.
uni-directional association
A uni-directional association is indicated by a solid line between the two classes. The class that knows nothing of the other class, has an open arrowhead pointing to it. A Lion uses Water, but not the other way around.

References

[1] Wikipedia - Class diagram
http://en.wikipedia.org/wiki/Class_diagram
[2] IBM Developer Works - UML basics The class diagram
https://www.ibm.com/developerworks/rational/library/content/RationalEdge/sep04/bell/
What's the difference between Aggregation and Composition?
http://randomthoughtsonjavaprogramming.blogspot.nl/2013/11/whats-difference-between-aggregation.html

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