Recurring events with timezone

Tobias König tobias.koenig at
Thu Oct 28 18:47:24 CEST 2010

On Thursday 28 October 2010 16:20:15 Georg C. F. Greve wrote:
> Hi Tobias,
Hej Georg,

> > Either the client, which creates the  recurring event, splits the event
> > up in two recurring events, one for each DST  mode. Then during
> > summertime a recurring event with 08:00 UTC is used and during winter
> > one with 07:00 UTC.
> How would that work?
I'm not familiar with the recurrence rules of the kolab format, but with ICal
one can specify quite sophisticated exceptions. So a german kolab client could 
split the above event into the two events:

 - recur on every day on 08:00 UTC from last sunday in march till last sunday 
in october
 - recur on every day on 07:00 UTC from last sunday in october till last 
sunday in march

(where 'last sunday in xyz' might be literal date values)

So only the client, which is creating this event, has to know about the 
specifics of this DST. All other clients see fixed UTC values where they just 
add their current DST offset. 

The question is how complex these DST rules are in the various country and if 
kolab format supports to express them as exceptions.

> And how would the clients know against which DST zone to adjust their local
> time, e.g. how does the Brazilian client know that it is supposed to take
> 07:00 UTC / 08:00 UTC based on the German DST zone?
The other clients (not the creator) just add their local DST offset to get the 
local time. The time of the event is bound to the creators timezone, right? So 
the local time for the other clients changes.

The Brazilian client would not have to care about German DST. It just shows 
the event which is currently 'active'. So from march till october the 08:00 
UTC event will be listed with the current Brazilian DST added and from october 
till march the 07:00 UTC will be listed with the current Brazilian DST added.

> As you are part of the Kontact side of things, which is the approach that
> would work best for the KDE PIM environment?
I'm not working on the calendaring part, so I can't really comment on what 
would fit best. But since we have a good timezone/date library, both 
conversions should be possible for us.

Tobias Koenig | tobias.koenig at
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel. Germany +49-30-521325470, Sweden (HQ) +46-563-540090
KDAB - Qt Experts - Platform-independent software solutions

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