title: A facebook-like-notification system in php
body: <p>How can I put in place a facebook-like-notification system:
   - A userA writes a message to the userB
   - A listener on the database routes the message to the userB
   - On the userB interface, the message appears instantly</p>
  
  <p>How can I do that in php?</p>
  
  <p>Thank you very much,</p>
  
  <p>Regards</p>