On 2019-02-19 19:35, Steve Allen wrote:
The scope of IANA tzdb is, in short, to provide a way for POSIX-like systems to convert between internal system clock time_t values and local civil time in a way where a single choice is valid for all history since 1970. This is reasonably well documented.
Regardless how well tzdb is documented, one cannot say that tzdb data is very systematic. Compare the case of Asia/Hanoi with that of Europe/Busingen. Europe/Busingen was introduced into tzdb on 2013-02-27; it differs from Europe/Berlin since 1970, but it agrees with Europe/Zurich and was linked to it ever since. Only five years later, Asia/Hanoi was added to backzone; it differs from Asia/Ho_Chi_Minh since 1970, but agrees with Asia/Bangkok since 1955. Why was Europe/Busingen not added to backzone as Asia/Hanoi was? Its history is known very precisely. Why was Asia/Hanoi not added as a link as Europe/Busingen was? It may well be that some changes in the theory file can be construed to explain the discrepancy, but I think that database data should reflect the current design principles, not their history. I may be a sloppy reader, but I do see what the theory.html file says about the two questions above. Michael Deckers.