Jean Louis <bugs@gnu.support> writes: > * Sterling Hooten <hoo...@gmail.com> [2023-01-27 09:06]: >> Offset >> Constant duration difference between times of two time scales >> (ISO). i.e., a quantity to combine with a time scale to produce >> a wall time. e.g., Nepal uses a +5:45 offset from the UTC time >> scale. > > I would be careful calling it constant as time offset is changing > depending of daylight saving time. It is not constant. > > Time offset time stamp may be derived from time zone time. I am sure > about this. > > Time zone time stamp cannot be unambiguously derived from time > offset. I am mostly sure about this. > >> What kinds of representations would a calendar system capable of >> handling timezones require? >> >> • Instant (fixed) >> • This is referring to an unambiguous moment in time >> • e.g., 2007-02-03T05:00:00.000Z >> • Offset (fixed) >> • This captures the idea of "when did it happen for the person who >> made the observation" >> • e.g., 2007-02-03T04:00:00.000+01:00 > > Offset is not that fixed, maybe from viewpoint of storage as maybe it > is considered fixed in it's representation, but you have to keep in > mind that time offset by it's definition is changing itself, suddenly, > depending of daylight saving and time zone. >
I think your misinterpreting the intent here. If you specify a timestamp with offset, it is fixed. It does not change with daylight savings or any other change in rules for a time zone. It does not even specify a time zone. While it is true that a specific location may have time zone changes or that the offset from UTC might change as a result of daylight savings, an offset specified in a times stamp does not change and is fixed. This is one of the limitaiton with using offset. I also think it is a mistake (which I've seen others suggest in this thread) to equate an offset as being an abbreviation for a time zone. For example, some have suggested things like +10000 being the same as AEST and both being abbreviations for Australia/Sydney outside of daylight savings periods. I think that is incorrect. +1000 is a fixed offset from UTC and while it may be the same offset used in a time zone abbreviation like AEST or in a full time zone specification like Australia/Sydney, it is not a time zone specification, only an offset for a specific point in time.
