Cathy,
No need to traverse, you can do something like
select o2.object_id,
o2.object_type,
x.object_id as object_id_two,
x.object_type as object_type_two
from acs_objects o2,
(select o.object_id,
tree_ancestor_keys(o.tree_sortkey) as ancestor_key,
o.object_type
from acs_objects o
where o.object_id = :object_id) x
where o2.tree_sortkey = x.ancestor_key
and o2.object_id in (select community_id
from dotlrn_communities_all)
Of course you can stil tweak that to optimize stuff but the idea is there.
