There is still a big confusion on what is left or right on a relationship. And considering the figure on Atmire's document (https://docs.google.com/document/d/1X0XsppZYOtPtbmq7yXwmu7FbMAfLxxOCONbw0_rl7jY/edit#heading=h.46e6ol5ak216):
When creating entities, we will still have this doubt what it should be the left or the right item. At the DB level, we will have something like this for "relationships":
What should be the proper left or right when I need to create my own Entities? My answer to this, at this precise moment, is it really doesn't matter. But if you pick one direction, you need to be consistent with that decision.
So, to ease this thinking, I would propose to rename some field names to make it more clear because the doubt it's still there. I would propose to rename lefts and rights to item_id_1 and item_id_2 (or better names) on the "relationship".
I'm relating two items (1 and 2), it should't matter what is left or right, because I will label their relation afterwards. And also one can consider viewing it on the opposite side. IMHO we should consider just items/entities on that equation, ignoring the left and right names. Relations can be named like "is[Item1]Of[Item2]" or "[Item1]Has[Item2]" or using any other verb. Has an example, If I choose Entity 1 to be a Publication and Entity 2 to be a Person, that relation could be labeled as isPublicationOfPerson or PublicationHasPerson (two different and opposite meanings for labeling those relations). I'm describing what Item1 is related to Item2.
I'm bringing this to discussion because it still isn't clear for everybody. Perhaps matter for DSpace8.