User management hints

Hi everyone. I'm new to Freeradius, and I would like to write a very simple user management php/mysql script, that should allow me to do some simple things: 1) create a user; 2) set expire date for a user; 3) disable user, automatically at expire date or manually if needed. I installed successfully freeradius with mysql on a debian box and tested a new user with radtest. I also began to study sql schema, but I can't find many information on internet about it. Can anyone you suggest me some good documentation, just to begin? Thank you very much. Regards. -- GP