UML question

From: Avner Ben (avner_at_skilldesign.com)
Date: 01/19/04 

Date: Mon, 19 Jan 2004 21:14:04 +0100

how does one express in a class diagram a qualified association where
the key is itself an object reference? This is a common case, e.g. a
map, keyed by an object (rather than string or integer). Common sense
tells me to leave the qualification rectangle blank and extend an
association from it. However, I am not sure this is a valid UML syntax.

        Avner.