Recurring events with timezone

Joon Radley joon at radleys.co.za
Wed Oct 20 10:30:33 CEST 2010


Hi Hendrik,

> 
> If i am in Johannesburg my Kontact can convert each start-time to the UTC time by using the stored time zone from germany and then convert it to the system local time.
> In october:
> german local 10 -> UTC 8 -> south africa local 10
> in november:
> german local 10 -> UTC 9 -> south africa local 11

Now lets turn this around, you create the event in Johannesburg and accordingly include the CAT time zone:

How will you now do the conversion for the German user with only the Johannesburg Time Zone information?
 
Best Regards

Joon Radley

Cell: +27 (0)83 368 8557
Fax: +27 (0)86 547 2353
E-mail: support at toltec.co.za
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On 20 Oct 2010, at 9:34 AM, Hendrik Helwich wrote:

> Am 20.10.2010 08:46, schrieb Joon Radley:
>> Hi Hendrik,
>> 
>> This is an excellent example. Your argument is that the incorrect conversion in the client of UTC ->  local time can be fixed by adding time zone information to the object.
>> 
>> Lets run a use case with this. User A is the creator of the object and is situated in Johannesburg. User B that shares the folder is situated in Germany (for the daylight savings time).
>> 
>> The problem is: UTC ->  User B local time is incorrect.
>> 
>> Your suggested solution is: User A Time Zone + User A Local Time ->  UTC ->  User B local time
>> 
>> UTC ->  User B local time conversion will still be broken, as you need User B TZ to fix the incorrect calculation. Thus by adding the User A TZ information to the object no problem is solved.
>> 
>> The only time when the TZ information will help is when User A and User B is in the same time zone and they both know it. All other user cases do not benefit from User A’s TZ information.
>> 
>> You are trying to fix a client “bug” by providing it with information, which will only be valid/helpful in very limited cases.
>> 
>> By fixing the UTC->  locale conversion you will fix all the use cases. The localtime function has never failed me. Is there a problem with it on your OS?
>>   
> 
> Hi Joon,
> 
> timzones are working fine on my OS :-) the UTC time can surely be used for single events/tasks. But it is possible to code recurring events in kolab so you must add timezones to the format even if they are complex. This is obvious i think. Otherwise it is not possible to fix this problem.
> 
> To the example:
> The correct way would be to make the kolab xml with timezone e.g. like this:
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <event version="1.0">
> <product-id>KOrganizer 3.5.9 (enterprise35 20100805.1161816), Kolab
> resource</product-id>
> <uid>libkcal-2077575338.372</uid>
> <sensitivity>public</sensitivity>
> <start-date>2010-10-19T10:00:00</start-date>
> <summary>Test</summary>
> <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 count="-1">sunday</day>
> 		</start-date>
> 		<end-date>
> 			<month>october</month>
> 			<day count="-1">sunday</day>
> 		</end-date>
> 	</daylight-saving-time>
> </timezone>
> <recurrence cycle="monthly" type="daynumber">
> 	<interval>1</interval>
> 	<daynumber>19</daynumber>
> 	<range type="none"></range>
> </recurrence>
> <end-date>2010-10-19T12:00:00</end-date>
> </event>
> 
> (I added the timezone block and changed start-date and end-date to the local times)
> My Kontact now can see that i am in the same time zone as it is stored in the event and does not need to convert the local times. It can show me the 10 o'clock start-time for all the year. It also can do the stored local -> UTC -> local conversion but this would be an identity function and will cause the same result.
> 
> If i am in Johannesburg my Kontact can convert each start-time to the UTC time by using the stored time zone from germany and then convert it to the system local time.
> In october:
> german local 10 -> UTC 8 -> south africa local 10
> in november:
> german local 10 -> UTC 9 -> south africa local 11
> 
> So this example could be calculated correctly. Without storing the time zone information of germany that could not be possible.
> 
> Greetings
> 
> Hendrik
> 
>> [..]
>>   
> 
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