Subject: RFC 2445 Q: is TZID broken?

From: Mark Swanson <[email-masked]>
Date: Wed, 22 Jan 2003 13:48:30 -0500

Hello,

There seems to be an issue with time zones:
(from the spec)

	"The specification of
        globally unique time zone identifiers is not addressed by this
        document and is left for future study."

Since I'm seeing various popular ICalendar implementations use their own 
formats, how can anything be expected to interoperate?

You obviously can not rely on GMT offset ("America/Phoenix" and 
"America/Denver" both have GMT-07:00, but differ in daylight savings 
behavior) so time zone identifiers are required.

Would a list of timezones for every available implementation be required? As 
well as a mapping between them all?

Anyone can see the time zones that ScheduleWorld uses by iterating through the 
available TimeZone.getAvailableIDs(). 

Thank you.

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From: John Stracke <[email-masked]>
Date: 22 Jan 2003 14:10:19 -0500

On Wed, 2003-01-22 at 13:48, Mark Swanson wrote:

    Since I'm seeing various popular ICalendar implementations use their
    own 
    formats, how can anything be expected to interoperate?

From section 4.2.19 of RFC-2445:

    An individual "VTIMEZONE" calendar
       component MUST be specified for each unique "TZID" parameter
    value
       specified in the iCalendar object.

In other words, even if a TZID starts with a "/", and so is nominally
global, its scope is still local to the VCALENDAR.

Global time zone identifiers are nearly impossible; at a minimum, they
would have to come with a timestamp, since time zone definitions change
over time.

-- 
/===============================================================\
|John Stracke        | http://www.centive.com |HTML OK          |
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---

From: Mark Swanson <[email-masked]>
Date: Wed, 22 Jan 2003 15:16:43 -0500

> would have to come with a timestamp, since time zone definitions change

Ah. I see the correlation to the offset and daylight savings. 

Thank you.

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