The details of the change were a little more involved: A NULL value was not possible, since the field is part of the primary key (which is always not NULL). Therefore, it was necessary to introduce an "identity_rel" (magic value -10) which serves as a special value, and it allows to use a fk to acs_rels.
These changes are now committed to the oacs-5-9 branch.
The Oracle version us quite different, it uses a ref-count instead of the "originating_rel_id", where the latter makes it easier to understand the whereabouts of the values and eases deletions, etc.
