This assignment is aimed to let you practice Security and Trust in Software Architecture design. Assume we are developing a management system for a library system. In this system, users can borrow and return books, managers can add and delete books from the system. Your work is to use the UML class diagram to design a role-based access control for this system. 

(1) Design the framework and draw the structure by using the UML class diagram . The designed framework should include at least three objects: book, user, manager.

(2) Based on the diagram, write no less than 200 words to explain how your designed structure conforms to at least three security principles for computer security. 

(3) The structure should demonstrate how access control is managed. Based on the diagram, please write no less than 100 words to explain how access control works.