Thoughts on python classes to represent an ebook reader

[math math]

Hi,

I hope there are people here with strong OOP experience.

Which classes would an object-oriented python programmer create for the design of a e-book reader for example? I am not really interested in the code, just the OOP classes that would come to one's mind for a task like this.

It should allow users to buy new e-books, view their list of purchased books and read the books.

I have made an attempt of class diagram here "http://imgur.com/9TR2Tlm" but I would be really glad to hear other opinions. I have not used any inheritance for example. I didn't know exactly where it would be handy and I also dont know if these classes are theoretically a good basis at all...

Thanks a lot for comments/feedback.
Felix