Yes, that's what the incremental map reduce indexes are used for. Each book would be a document, which you could query by any of those attributes. I'd store the

Yes, that's what the incremental map reduce indexes are used for. Each book would be a document, which you could query by any of those attributes. I'd store the fact that each user owns a book as it's own document, and then you can easily get a view of books by user, or of users by book.