Earlier quoted context omitted.
what relations does a relational db not help with? (i thought they were basically an implementation of the relational model).
Being a child of, being included in... You can of course manage all those relations in a relational database but the job is done by you, not by the database.
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?