We have developed a calendar for our extranet. Each week we update it with next week’s courses schedule for all teachers and students of the school. This also triggers the sending per email of ICS files to those users who chose that option.
Now, it almost always happens that there are last minute changes, so a need to do a new schedule update, hence a resend of the updated ICS.
Question: for the moment the user has to manually delete the events already imported into its calendar application. Is there a way for us to add some DELETE or UPDATE events into the user’s calendar? Does the ICS format allows that?
Once you get into trying to do updates or deletes (cancel) you are going beyond the iCalendar file format and entering the wonderful world of iCalendar Transport-Independent Interoperability Protocol (iTIP) and iCalendar Message-Based Interoperability Protocol (iMIP) see the Guide to Internet Calendaring tools.ietf.org/html/rfc3283
The best solution will depend on your clients system/s. If you are delivering calendars rather than individual events I would recommend going away from e-mail delivery and using a subscription model. Here is an example of a University doing just that, icalshare.com is another example. Obviously if you wanted personalised timetables you would need personal urls. You could fairly simply just publish the files you are currently sending by email to the web.
If you use the webcal:// instead of http some calendar clients e.g. Outlook 2007 will open it automatically and then keep it updated.
If you don’t want to use the subscription model and responses from clients are required I know that Outlook 2007, Windows Live Calendar and Google calendars can all talk iTIP/iMIP to each other, unfortunately I can’t find a good list of other clients that do. Apparently Thunderbird 3 was going to but it has been dropped (it will still require the lightening plugin).