Have the following in your library:

1. Different book types (paper, digital and audio)
   
2. Different storage media (Book shelf, Computer, iPad, Kindle)
   
3. The main library where it contains all the book with all the types
   
4. Ability sort the books (regardless of their type)
   

Bonus:
Add the following features:

1. Ability to store in multiple media (for instance Kindle and Computer)
   
2. Ability to search a book by its name (or a portion of its name)