Subject: [IPTEL] Proposed resolution of CPL time-switch issue

From: Jonathan Lennox <[email-masked]>
Date: Thu, 14 Sep 2000 21:05:50 -0400 (EDT)

There was enough dismay over the whole iCal time-switch issue that I've
(semi-reluctantly) agreed that it's too complicated for the base CPL spec.

Accordingly, my propsal is this.  Roll back the syntax of time-switch to the
version in the CPL draft -01 (the crontab-based syntax).  Simultaneously,
though, define a CPL extension which provides an ical-time-switch tag, which
would include the whole of the iCal recurrence spec as it appeared in CPL
draft -02.

Would this generally satisfy everyone?

(You may note that my text describing CPL extensions assumed this solution
in its list of suggested extensions.)

-- 
Jonathan Lennox
[email-masked]

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From: Jonathan Lennox <[email-masked]>
Date: Thu, 14 Sep 2000 22:17:06 -0400 (EDT)

On Thursday, September 14 2000, "Henning Schulzrinne" wrote to "Jonathan Lennox, [email-masked]" saying:

> Jonathan Lennox wrote:
> I disagree strongly. I thought we had agreed that a simplified version
> of the ical syntax, minus some of the by-rules, would be an easier road
> to upgrade later, rather than having two completely different
> specification rules.

One consideration that I think is very important, which held true for the
crontab-based proposal but which (as far as I can tell) doesn't hold true
for iCal, is that it should be possible to write (easily) an O(1) algorithm
that determines whether a given instant in time falls within a given time
range -- i.e., without having to iterate through all the time positions
prior to the current one.

I'm trying to work out what such an O(1) subset of iCal would be.  It's
clear that the "count" rule has to be eliminated, and "bysetpos".  Probably,
expanding by* rules would have to go as well, though I *think* contracting
ones can stay.  "interval" is tricky, but possibly doable; I'm not sure.

I could make the argument, though, that we would actually have an *easier*
time with future upgrades if our two time syntaxes were completely
different, rather than largely the same but with important and subtle
semantic differences.  Given that (it seems) the implementation of
iCal-subset and iCal-complete have to be quite different, and the inevitable
confusion of "okay, '<time freq="daily" byhour="5">' is illegal, but '<time
freq="daily" ical:byhour="5">' is fine"...well, it feels like an
interoperability and documentation nightmare.

Additionally, as JR pointed out earlier in the time-switch discussion, it's
not possible to express "first monday of the month" or using only
contracting rules; that needs an expanding rule.  By contrast, it's trivial
using the crontab syntax.

That said, if consensus is for a subset, we can subset, once we're
algorithmically sure of what that subset should be.

-- 
Jonathan Lennox
[email-masked]

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From: Henning Schulzrinne <[email-masked]>
Date: Thu, 14 Sep 2000 21:09:20 -0400

-- 
Henning Schulzrinne   http://www.cs.columbia.edu/~hgs