how to model object containment in relational

I have a list of base_objects and containers (a table for each: object_table (id, name) and container_table (id, name).

Containers contain objects. That's simple to model. However containers can also contain containers. Is there a cleaner way to represent that relationally than
join_table (container_id, container_or_object_id, flag) where flag says whether the containee is itself container or object.

Is there a good newsgroup for this type of question? Some sort of relational theory and modeling newgroup? :)

--
Asya Kamsky

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