The worst of the bad sweaters, a bizarrely mossy Cosby castaway, belongs to Jennifer Aniston's character in The Good Girl.

She said: "I'm still a bad girl." I still have that side of me, it's just in its place now. It belongs to Brad or our adventures.

While mapping an author element to an author instance isn't too bad, there's not grouping element, like authors, that makes it clear that each author belongs to a single collection in a Book instance.