There can be alot to it, usually your class model will consist of things like,
Job's, Task's, Schedules, Calendars ( for Localised Holidays etc ..) within
EJB 's Message Driven beans can be used to Asynchrously execute your tasks.
Generally your scheduler will be running in its own vm calling out to EJB's etc...
I've been asked to look into a J2EE JobScheduler for my compnay, if we endup
creating our own instead of buying one, I will share my design.
Regards,
TK.