<p><strong>How do I represent an aggregation relation between two classes in UML, such that each class has a link to the other class's interface, not the implementing class?</strong></p>

<p>E.g. I have a class Foo that implements iFoo, and Bar that implements iBar. Foo should have a member variable of type iBar, and Bar should have a member variable of type iFoo.</p>

<p>If I create an aggregation between the two implementing classes, then the member will be of the type of the implementing class, not the superclass. And aggregations between interfaces are invalid in UML (and don't make much sense).</p>

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If you need a border you can set:
```
```
ControlBox = false
Text = ""
```
```