Re: DTSTART for recurrence instances

[Bruce_Kahn@xxxxxxxxxxxxxxxx]

Craig wrote on 12/01/2003 08:07:59 PM:
> Suppose we have a recurring event for every Monday in January:
>  
> BEGIN:VEVENT
> SUMMARY:Every Monday in January
> DTSTART:20040105T100000Z
> DTEND:20040105T110000Z
> UID:A-Unique-ID
> RRULE:FREQ=WEEKLY;UNTIL=20040131T170000Z;
>  INTERVAL=1;BYDAY=MO;WKST=SU
> ...
> END:VEVENT
>  
> Now suppose we SEARCH for that event with Expand:TRUE:
>  
> BEGIN:VQUERY
> EXPAND:TRUE
> QUERY: SELECT * from VEVENT
>   WHERE UID = 'A-Unique-ID'
> END:VQUERY
>  
> What will be returned in the query?  

Per the CAP 12-e text, ALL instances
will be returned and as individual VEVENTs.  So the returned data
should look something like:

BEGIN:VEVENT
SUMMARY:Every Monday in January
DTSTART:20040105T100000Z
DTEND:20040105T110000Z
UID:A-Unique-ID
RECURRENCE-ID:20040105T100000Z
...
END:VEVENT
BEGIN:VEVENT
SUMMARY:Every Monday in January
DTSTART:20040112T100000Z
DTEND:20040112T110000Z
UID:A-Unique-ID
RECURRENCE-ID:20040112T100000Z
...
END:VEVENT
BEGIN:VEVENT
SUMMARY:Every Monday in January
DTSTART:20040119T100000Z
DTEND:20040119T110000Z
UID:A-Unique-ID
RECURRENCE-ID:20040119T100000Z
...
END:VEVENT
BEGIN:VEVENT
SUMMARY:Every Monday in January
DTSTART:20040126T100000Z
DTEND:20040126T110000Z
UID:A-Unique-ID
RECURRENCE-ID:20040126T100000Z
...
END:VEVENT

>              
                     
        Will the DTSTART 
> (and DTEND) of each recurrence instance be the
same as 
> the 'master' (as in column 1 below)?  

No.  (Please be careful using 'master'
as it introduces a new term w/o defining it.  I take it to mean the
initial instance defined by your original VEVENT (sans repeating and exclusion
grammar or RDATE / EXDATEs) but I could be slightly wrong.)

>              
                     
  Or will DTSTART and 
> DTEND have the 'effective' value for the recurrence
instance 
> (as in column 2 below)?  

Yes

> The expected result, intuitively and instinctively,
is Column 2.
> The prior discussion thread implied that Column
1 is correct 
> (along with some discussion explaining that this
is why DTSTART 
> is not always suitable for use in QUERYs, whereas
RECURRENCE-ID
> is more suitable).

I havent been able to keep on WG threads
lately so I didnt see that.  

The interpretation depends on how you
read the property defintions in 2445.  From my catchup attempts on
this thread (bottom up) it appears as if some grok the difference between
instance identifier (UID and RECURRENCE-ID) and instance starting time
(DTSTART) and some may not.   By correctly using each property as
its defined,  I dont see how one would say Column 1 (omitted) is the
correct answer but Ill go back and see if I missed something.

Essentially, the CUA needs to be smart
about when it uses EXPAND:TRUE in a VQUERY.  It depends on what the
CUA is attempting to do.

If you want to find a particular instance
of a component (ie: UID:A-Unique-ID) then you would include RECURRENCE-ID
to find it no matter where in time it exists and not use EXPAND (or use
EXPAND:FALSE).  

If you want to find all instances of
a component (ie: UID:A-Unique-ID) then you would omit any RECURRENCE-ID
and use EXPAND:TRUE.

If you want to find any entires during
a particular time range, say the work week starting 5-Jan-2004, (even those
NOT with UDI:A-Unique-ID) you would omit any UID or RECURRENCE-ID and not
use EXPAND (or use EXPAND:FALSE).

Its somewhat problematic if you do the
latter AND include EXPAND:TRUE as the results returned would violate the
WHERE constraints of the query.

Bruce
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Bruce Kahn                  
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