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UML : Aggregation + Multiplicity

I don't understand what the hollow diamond next to Class A together with the multiplicity next to Class B implies about the relationship between Class A and B. Could someone clarify this for me?

Geert Bellekens
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Walter Park
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1 Answers1

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  • Aggregation is a special type of Association.

  • The lives of both objects are independent of each other.

  • Both objects have their own life cycle.

  • Define the aggregation name.
  • The direction of the empty diamond specifies which object contains the other object.

For an example,

enter image description here

For your question,

I don't understand what the hollow diamond next to Class A together with the multiplicity next to Class B implies about the relationship between Class A and B. Could someone clarify this for me?

What the multiplicity does is every Class A objects associated with zero to many Class B objects and also the Class B depends on Class A but they both have their own life cycles like the example that i gave unlike Composition.

EDIT:

Like this ,

enter image description here

You have to specify in both sides whether how many objects involved with Class B objects.Like in 0..n in Class B side.

AVI
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    Correct me if I am wrong: Class A is an aggregate class made up of zero to many constituent Class B objects? – Walter Park Mar 12 '16 at 04:22
  • @WalterPark Yes, that's correct.I hope it make sense. – AVI Mar 12 '16 at 04:24
  • Sorry. I edited my earlier comment. Please take a look at it again. – Walter Park Mar 12 '16 at 04:34
  • @WalterPark yes, but you have to note that in Class A to show that 1 or n number of objects connected with 0 or n number of objects of Class B – AVI Mar 12 '16 at 04:35
  • @WalterPark If you figured that out, mark my answer as the accepted one – AVI Mar 12 '16 at 04:42
  • I do not understand what you are trying to say in "you have to note that in Class A to show that 1 or n number of objects connected with 0 or n number of objects of Class B." Could you please clarify. – Walter Park Mar 12 '16 at 04:42
  • @WalterPark I edited the answer. – AVI Mar 12 '16 at 04:48
  • Correct me if I am wrong: So in Class A you would have a field like **private Collection** which would latter be initialized in it's constructor as a List or Set. Whereas in Class B you would have no field relating to Class A. – Walter Park Mar 12 '16 at 06:34
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    @WalterPark: that is correct. A collection is one valid way to implement that multiplicity. However, note that in UML, the multiplicity is written as [0..*], or just [*]. It is never written with letters. – Jim L. Mar 12 '16 at 13:34