Using data base triggers will help
Hi
For your first question.
You will receive all the user requests; from that u can filter out reg and unreg commands.
Question no 2:
In give API u don't find such A functionality to send messages by listening for events. U can design ur system to listen such events and send messages. Check for observer pattern for more details.
I hope u got answer z
thanks
cheers
Amila Silva
Great ,let us know if u need any assistance.