Re: [Evolution] Calendar: recurrence, exceptions and occurrences

["D. D. Brierton" <darren dzr-web com>]

On Wed, 2004-03-03 at 14:55, Dan Winship wrote:

> Yeah, it doesn't seem to make much sense in this case, because the model
> assumes that you don't create exceptions at the time you create the
> appointment. Exceptions are the changes you make *after* the appointment
> is initially created. You're basically telling Evolution "I want this to
> happen four times. No, wait, cancel the middle two." (Maybe
> "cancellation" would be a better word to use here than "exception".)

The  trouble is that I can (and do below) give you real world examples
where what you want is an exception to the recurrence not a cancellation
of an occurrence. (That sentence may need to be read more than once!)

> In real life, you would never say "we will meet for the next four
> Wednesdays that are not 3/17 or 3/24". You would either say "we will
> meet on 3/10, 3/31, 4/7 and 4/14" or "we will meet every Wednesday from
> 3/10 to 4/14, except 3/17 and 3/24".

But surely, the second way is what the "until" (in combination with
"Exceptions") option in the Recurrence Rule is for. The "for" option
seems to precisely meet the first way, or at least that's what I
expected it to do.

Here's some real world examples:

Although I stopped being a full-time academic a few years ago now, I
still do teach a few classes here and there at the University. My
timetable for these classes tend to be one of two ways, both
corresponding to the two ways you mention above. Either I teach a class
weekly or twice-weekly for a whole term or semester; in which case I
start the appointment at the date and time of the first class and then
use the "until" option of the occurrence rule to mark the date of the
last class. Some of the classes will however fall on exam days or public
holidays, in which case I use the "Exceptions" to cancel those classes.

Some classes, however (and more than you would perhaps think), are of
this form: exactly four two-hour seminars to be taught, starting from
this date. During the first class it then transpires that some of the
students have exams on one of the subsequent weeks, and another class
falls on a public holiday. The exceptions in this case should simply
"push" the remaining appointments forward. I have, after all, specified
that this appointment is to recur for four times exactly.

I also have similar situations in my primary occupation. I may contract
to do four afternoons on site, on the same day over four weeks. However,
for some reason one week in the middle isn't possible. Again, in this
situation the exception is not intended to cancel one of the afternoons
I have contracted for, but merely postpone it.

I also have a non-work example -- I use Evo's appointments as an all
purpose reminder/diary. Let's say, purely hypothetically, that I am one
of those tremendously bad people who download American TV shows because
I am too impatient to wait for them to air in the UK. Now let's say that
one of these shows has 24 episodes, because, let's say, it takes place
over a 24 hour period, and starts on a certain date in October. So I
enter it into my calendar, and give it a recurrence of 24 occurrences.
But I also know that American TV shows go on hiatus (how do people put
up with that?), and so as I learn of these hiatuses I add them as
exceptions. The purpose of all this is so that I know whether an episode
is going to be available that week or not. I was^H^H^H would be
extremely surprised to suddenly discover that my calendar suddenly
thinks the show has already finished, because it treated those
exceptions as cancellations.

> Evolution doesn't let you say it
> the first way (though it could, using iCalendar RDATEs instead of
> RRULEs), but it does allow the second form.

In summary, I think that if you are using "until <date>" in your
recurrence rule then an exception should indeed be a cancellation.
However if you are using "for <n> occurrences" then an exception should
be a postponement.

What do you think?

Best, Darren

-- 
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D. D. Brierton            darren dzr-web com          www.dzr-web.com
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