Recurring events with timezone

Hendrik Helwich h.helwich at
Thu Oct 28 11:11:31 CEST 2010

Am Donnerstag, 28 Oktober 2010 10:58:55 schrieb Hendrik Helwich:
> Hi,
> thank you for the active discussion on the kolab tz issue :-)
> I think some interesting thoughts where argued here. But unfortunately i
> have to act now and i don't have the feeling something is going to change
> in the kolab format and the kolab clients with regard to the tz problem in
> the near future.
> So i think we will implement it like it is described below to be most
> interoperable between the kolab format and the iCalendar format.
> Unfortunately the shown times in evolution and kontact/outlook will be
> different for many recurring events due to the tz restrictions in the kolab
> format and also because of the discussed tz bug in kontact/toltec.
> Conversion iCalendar -> Kolab
> * convert the stored time & stored tz from iCalendar to an UTC time and
> store it in the kolab item.
> * Store the tz from the iCalendar in the kolab item. I created an attached
> an XML schema document which describes the structure and constraints of
> this timezone element.


I had to fix the schema. The actual version can be found here:

Best Regards,


> E.g. for the german tz:
> <timezone>
>         <id>Europe/Berlin</id>
>         <standard-time name="CET">
>                 <offset>+0100</offset>
>         </standard-time>
>         <daylight-saving-time name="CEST">
>                 <offset>+0200</offset>
>                 <start-date>
>                         <month>march</month>
>                         <day>sunday</day>
>                         <daynumber>-1</daynumber>
>                 </start-date>
>                 <end-date>
>                         <month>october</month>
>                         <day>sunday</day>
>                         <daynumber>-1</daynumber>
>                 </end-date>
>         </daylight-saving-time>
> </timezone>
> * So at least the time is shown correctly in kolab clients until the DST
> rules of the events tz or the users local tz does change.
> * timezone tag must be preserved by other kolab clients according to the
> kolab format specification [1].
> Conversion Kolab -> iCalendar
> * If the kolab format contains a timezone tag then convert it to an
> iCalendar timezone else use UTC timezone.
> * No conversion loss for kolab format here but we have a problem even for
> UTC timezone because of the discussed bug in the kolab clients. The shown
> time in the kolab clients and evolution can be different until the bug is
> not fixed. * Convert the stored UTC time to a time which has the stored tz.
> Best Regards,
> Hendrik
> [1]

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