calendar recurrence

Hi, I'm working on a calendar program that stores and recalls events. I'm having much fun figuring out how to represent the recurrence of events in the database :-) I'm sure this has been done before, although I'm not having much luck finding references to such information. Here is what a list of situations I can think of: Each event should have some basic information, like type, title, notes, begin date, and possibly and end date. I would like to be able to recur something like the following: * repeat [every|every other|every 3rd|every 4th] [day|week|month|year|M-F|M,W,F|T,Th|Sa,Su] or, * repeat on [1st|2nd|3rd|4th|last] [Sun|Mon|Tue|Wed|Thu|Fri] of the month every [month|other month|3 months|6 months|year] and either * always repeat or, * repeat until a given date. depending on how the data is represented, things like this may be an issue: * what if an event is repeated every day for a month, and the user wants to delete one of the recurrences from the middle? * what if the user selects one of the recurrences and changes the begin date to overlap one of the other recurrences? I guess one solution would be to not allow any editing of the recurrences of an event, but it would be nice to be able to do so. Thanks for any help & pointers. Monte