KEP2: Modification of datetime type, introduction of 'tz' =?utf-8?q?sub-tag=09?=(wiki revision 10645 of 2010-11-19)

Hendrik Helwich h.helwich at tarent.de
Mon Dec 20 15:22:36 CET 2010


Hi Joon,

Am Montag, 20. Dezember 2010 14:40:45 schrieb Joon Radley:
> On 20 Dec 2010, at 12:11 PM, Hendrik Helwich wrote:
> >> Canonically storing "UTC calculated from standard time" solves both, but
> >> for the second case the chance of bad results is just very tiny, whereas
> >> in the first case we're guaranteed to be wrong half the year - always
> >> the other one from when the event was created.
> >
> > i think it is not nice to store a wrong UTC time half the year. This is
> > complex and can confuse people.
> > Also technically it is possible that the standard time changes for a time
> > zone. This would break the hole concept.
> > I am not sure if this could happen in practice but from the format it is
> > possible.
> >
> > So if already a wrong UTC time is stored half the year it could also be
> > stored wrong for the hole year by storing directly the local time as UTC.
> > This will be less error-prone.
>
> How can UTC be wrong? Any conversion to UTC that give the wrong UTC needs
> to be re-implemented. (Visa versa is also true).

If the local -> UTC conversion does ignore the DST (like proposed by KEP 2) it 
will result in a wrong UTC time if the used time zone uses DST.

Best regards,
hendrik


> Best Regards
>
> Joon Radley
>
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