DTV — Date-Time Issue: Time Zones

13.5.4 "When there are two calendars for a time zone, one is standard time and the other is daylight savings time. The dates and time of day for changing between them is determined by local authorities for each time zone."

Said authorities do, on occasion, change not only the dates and time of day for changing between local calendars, but the time offsets that apply within a locale. I would like to see the example that demonstrates how this specification would be used to reason coherently about events both prior to and after such a time zone transition in a continuously operating system (no big-bang updates allowed).

Comment #2

The Annex B references do not include the Zoneinfo database, ftp://elsie.nci.nih.gov/pub/, http://en.wikipedia.org/wiki/Tz_database.

(Zoneinfo handles the situation mentioned in Comment #1 by making the locale identifier be the primary key. For example, if your time zone is America/New_York, then the different rules for Daylight Savings Time before and after the 2007 changeover are implicit in any conversion between local time and universal time.)

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