[andrewcooke]

but isn't the point of being able to implement any relationship you want rather than having a few particular kinds (child of, included in) "built in" a feature? are you going to extend your database every time someone wants a different kind of relationship?

[jclevy]

Yes, but usual relations could be implemented by default and generic relation still be available.

I just want to test this and see if the database can do more and my code less.