how to loop table every 1 second for no more than 4 seconds

I have a problem with PL/SQL stored procedure.

loop, checking the table every 1 second for no more than 4 seconds

   if response that one specifid field in table is changed, return a message

   if no response is found in 4 seconds, return a timeout error

Thanks in advance for any help Received on Sat Nov 25 2006 - 14:10:17 CST