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From: cjsv@cs.adfa.oz.au (Christopher J S Vance)
Newsgroups: comp.lang.ada
Subject: Re: Timezone/Daylight Savings time info in CALENDAR for Ada 9X...
Keywords: CALENDAR, Timezones, Daylight-savings-time
Message-ID: <438@ccadfa.oz>
Date: 31 Aug 89 01:21:46 GMT
References: <20800@sequent.UUCP>
Sender: news@ccadfa.oz
Organization: Computer Science, Univ. of NSW, ADFA Canberra, Australia
List-Id: <comp.lang.ada>

In article <20800@sequent.UUCP> paulr@sequent.UUCP (Paul Reger) writes:
.> package.  Or maybe have information that will name the 24 time zones
.> in the world and have a function to return what the name of the local
.> time is.

-12 hours ...  +12 hours gives 25 time zones.  Now add all those places
where the difference from UTC is not an integral number of hours.  How
many now? Does Saudi Arabia still use solar time (midnight at sunset?)
-- that one varies a lot.  The ISO standard `name' of my timezone is
`+1000', meaning 10 hours ahead of UTC, but other parts of Australia
(including external territories) are on +0630, +0700, +0800, +0930,
+1030 and +1130.  And there are even more time zones in summer, because
some of the country changes, while the rest doesn't. 

If you want to use parochial names for timezones like PST, PDT, etc.,
then you've made it impossible for Ada to work outside USA.  Does `BST'
mean Bering Standard Time (if it still exists?) or British Summer Time?
Just because Bering Time was/is used in Alaska doesn't mean all of your
NATO places in the UK should get the time wrong all summer, does it?

Using ISO names makes it much easier for your package to work
world-wide.  But you still have to include the minutes, not just hours.
And it's not even tied to the English language for time zones.

.>     2. Daylight savings time.  This varies from Country to Country,
.> but it would still be useful for implementations to give this type of
.> information.  (I do not know precisely what I am suggesting an
.> implementation do with this information, but it would be useful
.> nonetheless.)

And from part-to-part of the same country.  Parts of Australia do not
have DST, and there's no guarantee those that do will do so at the same
time. 

A while back, a package was posted to provide exactly the sort of thing
you want, but it was in C for Unix.  Maybe Ada can learn from the rest
of the world.