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a.
Bi-directional
Bi-directional is a relation among two classes where each class
requires to access attributes from another class and vice versa.
b.
Directional
Directional happens
when a class requires another class’s
attribute; otherwise the other class does not.
Image 2.10 Association Relationship Diagram Illustration
(Source: System Analysis and Design Method – Whitten and Bentley,
2007)
3.
Aggregation/Composition
In several cases, there are some classes that made up of another
class. This kind of relationship relates from the
larger “whole” class
in which contains one or smaller “parts” classes, and yet this kind of
relation distinct into 2 different relations:
a.
Aggregation
Aggregation happens when there is an object that can’t be
shaped unless other objects have been constructed beforehand.
In UML diagram, aggregation is drawn with a hollow diamond.
However according to Whitten and Bentley (2007), in UML 2.0
aggregation relationship is not used anymore due to its
meaningless form comparing to Composition.
b.
Composition
Composition is the stronger model of aggregation. In
composition,
if the “whole” class is vanished, thus all smaller
“parts” classes would be vanished as well, whereas
it would not
be happened in aggregation.
In UML diagram, aggregation is
drawn with a filled diamond.
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