Role::
Role_ID: the ID of a role (Primary Key)
Role_Name: the Name of a role
Priviliage: the priviliage granted to arole
User::
u_Name: name of user (Primary Key)
passwd: password of user
u_type: student/teacher/author/administrator
Grants::
u_Name: name of user
priviliage: a priviliage granted to a user(abstract/wave/present/add_tool/...)
User_profile::
u_Name: name of user
Book_ID: the books'd ID the user involved(learning, teaching or written)