Re: Status of the CALSCH working group (Alarms/SEQUENCE)

[Bruce_Kahn@xxxxxxxxxxxxxxxx]

Doug wrote on 11/07/2003 04:14:11 PM:
> > Alarms/SEQUENCE -- I remain confused: Can there be two identical
> > objects in the same calendar? If not, we should clearly say so.
> 
> You can and iCAL has no such restriction on any component including
VALARMs.

Sorry, iCalendar does state that multiple
repeat instances at the same date/time are to be considered one:

               
                     
                    Where
   duplicate instances are generated by the "RRULE" and
"RDATE"
   properties, only one recurrence is considered. Duplicate instances
   are ignored.

at least 4 times.  There is also
:

   4.  When the combination of the
"RRULE" and "RDATE" properties on an
       iCalendar object produces multiple instances having
the same
       start date/time, they should be collapsed to, and
considered as,
       a single instance.

in case you missed the other occurances.
 

You also expliclty restrictions in CAP
with:

   There MUST NOT BE more than one "BOOKED"
state object in a calendar
   for the same "UID". The "ADD" method value
may create multiple
   objects all in the "BOOKED" state for the same UID, however
for the
   purpose of this memo, they are the same object that simply have
   multiple "VCALENDAR" components.

Essentially this says that there can
not be any identical VEVENTS with the same identifier that are BOOKD.  Its
interesting to note that CAP disallows it with "MUST NOT" but
then goes on to say "may".   The first line was correct,
the later text removes the restriction of sorts and is bad.

I have yet to hear any good justification
for allowing "identical but separate" VALARMs that match any
practical view of things.  Despite Dougs and Marks claim, the only
reason to have SEQUENCE (or ALARMID) on VALARMs is for this rare usage
case that currently noone actually has nor models anyones actual behaviour
or needs.  Id like to apply KISS to this and move CAP along...  (Just
like we disallow multiple copies of the same booked entry, the same should
go for alarms).

> Currently all components have a unique identifier
within their context 
> of usage.

Not totally true.  An example of
this is VDAYLIGHTs and VSTANDARDs in a VTIMEZONE.  The TZID of the
VTIMEZONE is unique but the TZNAME (akin to its identifier) is not unique.
 In fact the correct VDAYLIGHT/VSTANDARD is found by selecting the
subcomponent criteria that meet the requestors needs (ie: when its in effect).

The ONLY case that seems to be demonstratable
for SEQUENCE (nay, ALARMID) is the case where there are multiple, identical
VALARMs whose existance is somewhat questionable, at least for me.

Bruce
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Bruce Kahn                  
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