Association and constraint question

Hi there!

I would like to ask you about the following situation:

There is a class named A. It contains (aggregation) two classes (B and C), but they didn’t inherited from a common class.
Is it possible to associate B and C to A and use a constraint with {or}?
An other solution could be use of interface (Iface), so I can associate A with Iface, B and C can realise Iface.
But the question is that can I use constraint for this?
(as I found, associating B and C to A means that A will contain a reference for B and an other reference for A).

Thank you,