I have no such experience in developing an embeded library system.
I think you should work with database management system such like as mySql. That mean, you should create an library database in mySql, in which you will have some table such like book Table and User Table and so on. Now you should write your program that can work with mySql so that you can visite the library system and get the data what you want and change them and insert some new data.
I think you can also work without DBMS, that mean you can use your file system, but you should do more in it.