Hello everyone! i'm new in this forum, hope to be educated from it :)

i have a question mostly about designing in java.

i have this project i have to do that suppose to simulate an online book store (like amazon for example).

I'm going to use a server\client architecture (not a web application).

my main question is how to design the class diagram.
i need the GUI, DB handling methods, but i don't know how to connect between them, how will my class diagram will look.

am i suppose to make a class for every screen i will have for the user, and do i need classes for example for:book,user and so on?
and if so what is the connection between them?

what is the standard for that sort of project?

i would really appreciate some help that will push me forward a step.