I'm trying to use PHP to grab calendar information from Exchange 2007 to display the calendar on a webpage. I've figure out how to do all of this with EWS but I was wondering if there is a way to get updates to the calendar in real time so that they are changed on the website instantly. Can Exchange trigger my script whenever a change is made or do I need to poll Exchange at regular intervals? If the latter, is that going to tie up resources?