Don,
I like using the object_id but the problem is updates on an
existing site where the heirarchy was created with the old
style key mechanism
Node ObjID Context SortKey
A 1 null 1
B 2 1 1.1
C 3 null 2
If you wanted to update B's context_id to null you couldn't assume
it's object_id was available since it had been used by C for its sortkey.
Of course on insert it should be ok (although it's conceivable that if
a site juggled it's context_ids around enough the tree_sortkey could
have walked past the object_id sequence but I don't think that it has
ever or would ever happen). To be certain and safe though you would
need to bump the object_id past the max tree_sortkey if it had, and
when updating context_id to null you would need to take a
nextval(object_id) although use it just for the sortkey rather than as
the actual object_id.
