[Tagging] opening hours

[Greg Troxel]

This points to the RFC

  http://en.wikipedia.org/wiki/ICalendar

which is

  http://tools.ietf.org/html/rfc5545


I created a test event, which starts in march and is 1000-1200 local
time on the third sunday of every month.  Here's the ics file from the
mac calendar.  Obviously there's a lot more in here than is needed to
specify the time - I'l annotate it

  BEGIN:VCALENDAR
  VERSION:2.0
  PRODID:-//Apple Inc.//iCal 4.0.1//EN
  CALSCALE:GREGORIAN

we can skip this..

  BEGIN:VTIMEZONE
  TZID:US/Eastern
  BEGIN:DAYLIGHT
  TZOFFSETFROM:-0500
  RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
  DTSTART:20070311T020000
  TZNAME:EDT
  TZOFFSETTO:-0400
  END:DAYLIGHT
  BEGIN:STANDARD
  TZOFFSETFROM:-0400
  RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
  DTSTART:20071104T020000
  TZNAME:EST
  TZOFFSETTO:-0500
  END:STANDARD
  END:VTIMEZONE

This is all about the timezone, and that's something OSM already ignores
(times are in the local time at the location), which seems perfectly ok.

  BEGIN:VEVENT
  CREATED:20100221T124320Z
  UID:2D391E0D-310E-4B54-8A98-DCEE2F16F74F

that's even metadata to let sent/received invitations match up, so not needed

  DTEND;TZID=US/Eastern:20100321T120000

end time (first due to alphabetizing

  RRULE:FREQ=MONTHLY;INTERVAL=1;BYDAY=3SU

the recurrence rule.

  TRANSP:OPAQUE
  SUMMARY:TEST EVENT

  DTSTART;TZID=US/Eastern:20100321T100000

start time of first event

  DTSTAMP:20100221T124356Z

perhaps created on export; not needed

  SEQUENCE:6

not sure what that is

  END:VEVENT

  END:VCALENDAR



Clearly opening hours more or less has a grammar (I wonder if anyone is
trying to mcahine parse the values, and finding problems, or has a "find
me an open foo nearby" service).

The current rules are geared towards weekly recurrence, which is of
course a good match for (much of?) the real world.

In vcalendar, there can be "third sunday" rules and "every two weeks".
It seems likely that only "third sunday" or "last thursday" is needed
for opening hours.

So using

  Su[3] 10:00-12:00

for third sunday, and

  Th[-1] 10:00-12:00

for last thursday, plus

  We[-2] 19:00-21:00

for penultimate wednesday (I know a place that gives ham radio exams on
that actual schedule) would be minimally invasive to the current format
and still capture the semantics of icalendar.






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