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association and aggregation

 
sam liya
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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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Use code tags for code, quote tags for quotes.
 
Hong Anderson
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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.
 
David Newton
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Quote tags, when done correctly, should look like this:
I wrote:Use code tags for code, quote tags for quotes.
 
Ilja Preuss
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What is meant is that an instance cannot aggregate itself, neither directly nor indirectly.
 
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