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association and aggregation

sam liya
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Joined: Nov 25, 2008
Posts: 1161
i got this from internet .

Aggregation [...] is the typical whole/part relationship. This is exactly the same as an association with the exception that instances cannot have cyclic aggregation relationships



I can't understand what is mean by

that instances cannot have cyclic aggregation relationships
David Newton
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Rancher

Joined: Sep 29, 2008
Posts: 12617

Use code tags for code, quote tags for quotes.
Hong Anderson
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Joined: Jul 05, 2005
Posts: 1936
Actually the UML specification doesn't disallow that. But in reality, there shouldn't be any objects that aggregate each other.
Could you give an example?

Anyway, don't trust every thing on internet, (including my post of course) if you want to know about UML, the most trustworthy resources are UML specifications from OMG.


SCJA 1.0, SCJP 1.4, SCWCD 1.4, SCBCD 1.3, SCJP 5.0, SCEA 5, SCBCD 5; OCUP - Fundamental, Intermediate and Advanced; IBM Certified Solution Designer - OOAD, vUML 2; SpringSource Certified Spring Professional
David Newton
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Rancher

Joined: Sep 29, 2008
Posts: 12617

Quote tags, when done correctly, should look like this:
I wrote:Use code tags for code, quote tags for quotes.
Ilja Preuss
author
Sheriff

Joined: Jul 11, 2001
Posts: 14112
What is meant is that an instance cannot aggregate itself, neither directly nor indirectly.


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subject: association and aggregation