Recurring events with timezone

Bernhard Reiter bernhard at
Wed Oct 13 10:57:33 CEST 2010

Am Montag, 11. Oktober 2010 17:05:22 schrieb Gunnar Wrobel:
> Zitat von Hendrik Helwich <h.helwich at>:

> > Then kolab would only work when
> > all people are in the same timezone. I can not believe that :-)
> No, sorry, now I was imprecise :) What I meant was only specific to a  
> recurring event that crosses a change in DST. The client calculates  
> the time of the recurrence start based on the UTC start date and then  
> assumes local DST rules for the starting time of following events.

Gunnar's description matches what I remember. So it works for different 
timezones including the daylight saving changes.

I remember having discussions with our format designers (Joon, Bo) and the 
iCalender experts from KDE (Cornelius and Reinhold) about if this leaves a 
corner case broken. I did not convince them, though, and we left it be.
My point was that if there are two timezones where daylight time shifting 
happens at two different dates, the above calculation would not fully work.
Digging the archives (of formats and devel) should be helpful for the 

As for the solution, best would be a full analysis of all cases and arguments
so see if we really want them. I have a feeling that just adding extra options 
will not be enough as all clients will have to support them. The overview 
should be able to be done quickly, once all past discussions are found and 

To through in a complication: Depending on the solution for appointments
and their relations we might just have client create one UTC appointment
for each period where the distance to UTC does not change and relate
all of those appointments to each other. We need to have a solution for this 
coupling anyway, because of a number of issues with exceptions in recurring 

Till's post is about perserving the timezone of the place where the 
appointment will be as opposed to determining when it is. 
Example: I am in Germany, but I will travel to Milwaukee for a meeting
so the meeting will take place in CST, though I ran my client in CEST.
Till asked the question if that information when the meeting is in meeting 
space time is relevant to be saved. This is a completely different question
to what was discussed before.


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