[jerf]

Are you claiming the parents will always be unique? Because as the article says, you can easily have this, where going to the right is a parent relationship:

                  -> Line -> Verse -> Poem
    char -> Word
                  -> Clause -> Sentence -> Poem

You can try adding a further constraint that any given property must have only one path, so you can then recurse over the tree and find the one match, but as your model gets richer you will find that breaks.

And it's that last clause that is the killer for pretty much anything: "As your model gets richer you will find that breaks."

Plus the UI experience for that is awful. "I want to add this property to this Line but you're telling me it's a duplicate for some particular character? What the hell does that mean? I'm not adding a property to the character!" etc. etc.