[tz] tzdb timezone names/identifiers and links

Martin Burnicki martin.burnicki at meinberg.de
Fri Mar 1 11:35:25 UTC 2019

Guy Harris wrote:
> On Mar 1, 2019, at 2:41 AM, Martin Burnicki <martin.burnicki at meinberg.de> wrote:
>> With "location name" I just meant mean what is displayed to the ordinary
>> user, which eventually is even localized.
>> For users in Germany Düsseldorf, Hamburg, Munich or Berlin is fine, but
>> Stockholm probably not since users are not sure if Stockholm has the
>> same TZ rules as Germany.
> Well, that pretty much shows that tzdb IDs are not the right answer, given that users might not know that, for example, Hanoi has (since 1970) the same offset and summer time rules as Bangkok.  It even says that mapping from a tzdb ID to something "more friendly" won't work in those cases.

That's what I'm trying to say all the time. ;-)

> So, if a user really wants to know what time zone rules are being invoked at the current location, we need a way to describe them that wouldn't be meaningless noise to a user, e.g.
> 	{name} summer time rules
> with {name} being the name of an appropriate region - probably including the country you're currently in, but that isn't sufficient in many cases - and "summer time rules" appropriately localized, e.g. "Daylight Saving Time rules" in the US.

I fully agree. This would be very helpful.

For example, in earlier Windows versions (since Windows NT) there was
only a single DST rule for a particular zone, and there was not even a
way for an ordinary user to find out *when* DST would start and end for
the zone he had selected. You could only find this out if you looked
into the registry and tried to interpret the values correctly.

This is why the monitor program we (Meinberg) ship with the driver
software for our PCI cards on Windows (since Windows NT) has a tab that
shows these Windows-specific settings, so a user can check if the
settings are as expected, and the system will switch to or from DST at
the correct instance.

> {name}, as indicated above, is not something that can be looked up in a table given only a tzdb ID; you'd also need some indication of your physical location, so you'd get
> 	German summer time rules
> in Berlin, Düsseldorf, Hamburg, Munich, etc. and
> 	Swedish summer time rules
> in Stockholm, Gothenburg, Uppsala, etc., and so on.
> Or you could just dump out the rules - but one of the good things about the tzdb is that it reduces the chances that you need to *know* the rules, so dumping out the rules might be telling the user something they don't know and don't even want to know.

Yes, and I think this should me enforced more by making the "ID name"
less readable, so developers can see that they must not use them
directly but do some mapping before.

Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: martin.burnicki at meinberg.de
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