Assumptions:
    1. This is a one time run system.
    2. Once we exit the system, whole database is erased away.
    3. Firstly Librarian has to Login with Id= "admin" and Password = "admin", after that he can add new users and books. Now Librarian may LOGOUT.
    4. After adding certain data, users which were added now Login to their page.
    5. Remember, no user should exit the system.