Subject: RE: Duration: Does 1 day == 24 hours?

From: [email-masked]
Date: Wed, 28 Mar 2001 15:56:47 -0600

> > That cannot be inferred from the text, though.
> >
> > I think it definitely CAN be inferred from the text.
> 
> How? Where is the text that implies that P1D is not the same 
> thing as PT24H?
> 
> > Even in the syntax, there is the ability to differentiate 
> the DURATION
> > values into a choice of those based on the date, time or 
> week scales.
> 
> But the units used on the different scales are 
> interconvertible, meaning that
> the different scales can be treated as equivalent.  Unless 
> you can point to
> text that says otherwise, it is entirely reasonable to assume 
> they *are*
> equivalent.

The iCalendar text says that the date value type is based on a calendar day.
It also references ISO8601 in the date and date-time sections to specify
that the format is based on the representations defined in this standard. If
I can't find enough text in one specification I check the references (i.e.,
ISO8601). My read of the definition of calendar date in ISO8601 was that the
day was not so much defined as a 24H period but as a calendar unit of a
week, month and year. 

Hence, an event duration of one day means that the event ends at the end of
the day. 

Let's think about other calendar components that use DURATION (i.e..,
VTODO). If you specify an action item is assigned to you for today and
duration is one day, then that tells me that you should be done with it
today, not the end of tomorrow. Remember that the ends are not inclusive.
Right?

-- Frank

---

From: John Stracke <[email-masked]>
Date: Wed, 28 Mar 2001 17:32:36 -0500

> The iCalendar text says that the date value type is based on a calendar day.

Are you talking about 4.3.4, "This value type is used to identify values that
contain a calendar date."? But, again, that's just the data type; it doesn't
define the semantics.

> that the format is based on the representations defined in this standard.

So? Representation does not imply semantics.  I could reference ISO8601 and say
I want to use its representation, but the Julian calendar (as in per-Gregorian,
not Julian dates).  The semantics would be wildly different.

> If
> ISO8601)

(That's a side problem, by the way; I dislike having a normative reference to a
document where, when I try to request it, ISO asks me for $60.  I've gone to
the URL Alan posted, and I've read it; but, if I hadn't had that URL, I
wouldn't have guessed that it was available for free.)

> My read of the definition of calendar date in ISO8601 was that the

OK, I think we're nearing the problem here: as far as I can see, scheduling an
event for a date, with no time, makes no sense.  Actual events occur in actual
periods of time.  That period might be "midnight to midnight, 28 Mar. 2001,
EST", but it's still a period of time.  What extra capabilities do we get out
of supporting DATE values?

--
/=================================================================\
|John Stracke    | http://www.ecal.com |My opinions are my own.   |
|Chief Scientist |================================================|
|eCal Corp.      |"The Elliot 903 was the first portable I ever   |
[email-masked]|used, though it needed a furniture van to *make*|
|                |it portable." --Will Rose                       |
\=================================================================/

---

From: "Shannon J. Clark" <[email-masked]>
Date: Wed, 28 Mar 2001 17:24:03 -0600

On possible set of functionality for DATE values would be "events" of the
following form:

Days on/off duty
Days on vacation - especially for someone on a non-standard schedule (i.e.
third shift - the "day" might start at 8:00PM) - so there is value in a
concept of "I'm taking the next 4 days off" - which may make more logical
sense to most users than "I'm off for the next 96 hrs"

Work schedules in general are cases that always START and END at the same
point in time - so must accommodate the DST issues when 24hrs (or equivalent
in seconds) is NOT equal to "a day" - some work related occurrence have
durations measured in days - i.e. a Resident's shift at a hospital or a
Fireman's schedule.

There are also other types of long ranging events that might take place over
many days (a bike race, "sweeps" week etc.)

Hope this helps,

Shannon

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of John Stracke
Sent: Wednesday, March 28, 2001 4:33 PM
To: [email-masked]
Subject: Re: Duration: Does 1 day == 24 hours?

> The iCalendar text says that the date value type is based on a calendar
day.

Are you talking about 4.3.4, "This value type is used to identify values
that
contain a calendar date."? But, again, that's just the data type; it doesn't
define the semantics.

> that the format is based on the representations defined in this standard.

So? Representation does not imply semantics.  I could reference ISO8601 and
say
I want to use its representation, but the Julian calendar (as in
per-Gregorian,
not Julian dates).  The semantics would be wildly different.

> I can't find enough text in one specification I check the references
(i.e.,

(That's a side problem, by the way; I dislike having a normative reference
to a
document where, when I try to request it, ISO asks me for $60.  I've gone to
the URL Alan posted, and I've read it; but, if I hadn't had that URL, I
wouldn't have guessed that it was available for free.)

> day was not so much defined as a 24H period but as a calendar unit of a

OK, I think we're nearing the problem here: as far as I can see, scheduling
an
event for a date, with no time, makes no sense.  Actual events occur in
actual
periods of time.  That period might be "midnight to midnight, 28 Mar. 2001,
EST", but it's still a period of time.  What extra capabilities do we get
out
of supporting DATE values?

---

From: "Graham Gilmore" <[email-masked]>
Date: Wed, 28 Mar 2001 18:53:12 -0500

> of supporting DATE values?

    We've been here before.

    DATE value types are perfect for things like birthdays, holidays,
and other such types of events.  These types of events don't really have
an associated timezone, and often are "in effect" for the entire
duration of the day ( i.e. P1D :P ).  Alternatively they are useful to
specify the date on which a particular instant of time occurs, without
knowing or needing the exact time of day at which it occurs - for
example, I might have a note in my calendar which informs me that on
March 31st, a colleague returns from an overseas trip.

    Graham

---

From: Patrik Fältström <[email-masked]>
Date: Thu, 29 Mar 2001 07:18:17 +0200

>day was not so much defined as a 24H period but as a calendar unit of a

Exactly.

>Hence, an event duration of one day means that the event ends at the end of

Only if it starts at the beginning of the same day.

   paf