To further understand about Job Scheduler, you can refer the following links:
http://www.quartz-scheduler.org/
http://en.wikipedia.org/wiki/Job_scheduler
http://www.theserverside.com/news/1364726/Job-Scheduling-in-J2EE-Applications
http://technet.microsoft.com/en-us/library/cc720070%28WS.10%29.aspx