To be honest, I do not exactly understand your question. I talk about attribute of a class which allows me to specify additional relations or type ezobjectrelation.
Maybe you haven't noticed that, but there are two independent datatypes for that: object relation (singular) and object relations (plural). I believe the latter one is what you're looking for:
http://ez.no/doc/ez_publish/technical_manual/4_0/reference/datatypes/object_relations Hope this is it.
