2. Books can have some taxonomy data. For example, I could see a list of main characters which were presented in the book until the page I have read. I can see

2. Books can have some taxonomy data. For example, I could see a list of main characters which were presented in the book until the page I have read. I can see their short description, their relationship, or even where are they currently. You don't even need the book to do this explicitly. Having the app reference Wikipedia based on content read would probably serve as a good 90% implementation.