Let's say we have an index filled with publisher documents. A publisher has a collection of books, and
each book has a title, a published flag, and a collection of genre scores. A genre_score represents how well
a particular book matches a particular genre, or in this case a genre_id.
First, let's define some mappings (for simplicity, we will only be explicit about the nested types):
curl -XPUT 'localhost:9200/book_index' -d '
{
"mappings": {