Re: Date & Time problems

Neill Massello <massello@xxxxxxxxxxx> wrote:

David Empson <dempson@xxxxxxxxxxxxx> wrote:

Apple should provide a supported method of adding more cities.

But then they might as well just provide an optional dialog in which the
user can enter the offset and the daylight saving time dates manually.

That would be even better, but it isn't practical given the underlying
system implementation. You would need to be able to specify the entire
set of rules (including historical ones) for the time zone.

The underlying mechanism is a set of files in /usr/share/zoneinfo, which
contain a lookup table of all "transition points" at which the local
time changed relative to UTC (for all known time zones). It can be used
to find the local time for any UTC time within the supported range of
years (about 1900 to 2038), for any time zone, assuming no future rule
changes.

The zoneinfo system is reasonably standardised, and it has an official
source of rules which is regularly updated. One problem is that Apple is
tardy about updating their distribution to keep in sync with the
official source.

A second problem is that the zoneinfo files have a lot of time zones for
which Apple hasn't provided the user interface to select them. They
should either add ALL the missing cities/zones in System Preferences, or
provide a method for the user to be able to pick a time zone by its name
in the zoneinfo database (and perhaps manually enter the preferred city
name and its geographical location, though this is a minor detail).

There appears to be a difference in policy regarding city names. For
example, in New Zealand's case, System Preferences lets you pick
Wellington (our capital city) to get the NZ time zone. The underlying
zoneinfo file is Pacific/Auckland.

The names of the zoneinfo files are usually based on the largest city in
the time zone, whereas Apple seems to prefer the capital city (at least
in some cases).

A third problem is Mac OS X's reliance on the ICU database maintained by
IBM, which contains a separate copy of the zoneinfo rules (it is located
in /usr/share/icu). This has to be updated in sync with the zoneinfo
files, but actually making changes to this database is not an easy
operation (it involves a patched copy of the 'zic' tool for constructing
zoneinfo files, for example). This makes it difficult for end users to
update Mac OS X's time zone rules, and it means that Apple has an even
greater responsibility to keep them up to date on a prompt and regular
basis.

If they insist on continuing with ICU, the only acceptable way for Apple
to handle this is for them to start doing regular and prompt "Daylight
Saving updates" in a similar manner to how they do security updates.

Ideally, they should also be decoupled them from minor Mac OS X
releases, since people on dial-up Internet connections cannot
realistically download a 100 MB or larger system update just so they can
install a daylight saving update.

An even better solution would be to eliminate the use of ICU for time
zone rules and standardise the system on the zoneinfo files. This would
mean that the end user can update the rules themselves using the 'zic'
tool, which is supplied with Mac OS X. In this case, Apple should still
update daylight saving rules themselves on a regular basis, for
non-technical Mac users.

The way Apple currently handles time zones is an example of making
things more complicated by trying to make them too simple.

I agree entirely. The scheme they use at present is completely broken.
I'm not surprised that Apple isn't making inroads into the corporate/IT
realm when they mishandle things like daylight saving so badly.

(See my article at http://www.welmac.org.nz/nzdst2007.php for further
details.)

--
David Empson
dempson@xxxxxxxxxxxxx
.

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