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Subject: Recurrence in Intervals and Gluons
I have been attempting to constrain the iCalendar semantic constructs that are allowed in Intervals and Gluons. Recently there has been pushback, as availability, and freebusy have crept back in to Gluons, at least. Recent examples coming from EMIX clearly indicate that recurrence rules need to re-appear. ?1) It may be that they should be constrained to appear only in the Gluon, but not in the Interval. I would welcome conversation on that ?2) I think that the recurrence rule is applied through the Designated Interval – and is illegal in all other intervals (see ?1). The entire sequence, then, recurs based upon the rules applied to the Designated Interval start time. ?3) Is it legal to have a recurrence pattern that is shorter than the duration of the entire sequence? ?4) Time-of day based occurrences that include the leap forward and fall back hours are problematic. Is it legal to have a recurrence that spans such days? ?5) I can imagine a “hint” that says compute start and end times assuming a 24 hour day, and them compute run durations in a second pass taking into account leap days; it could work, but it seems awkward. More awkward than the other options? Well… tc The recurrence rule, if specified, is used in computing the recurrence set. The recurrence set is the complete set of recurrence instances for a calendar component. The recurrence set isgenerated by considering the initial "DTSTART" property along withthe "RRULE", "RDATE", "EXDATE" and "EXRULE" properties containedwithin the iCalendar object. The "DTSTART" property defines the firstinstance in the recurrence set. Multiple instances of the "RRULE" and"EXRULE" properties can also be specified to define moresophisticated recurrence sets. The final recurrence set is generatedby gathering all of the start date/times generated by any of thespecified "RRULE" and "RDATE" properties, and excluding any startdate/times which fall within the union of start date/times generatedby any specified "EXRULE" and "EXDATE" properties. This implies thatstart date/times within exclusion related properties (i.e., "EXDATE"and "EXRULE") take precedence over those specified by inclusionproperties (i.e., "RDATE" and "RRULE"). Where duplicate instances aregenerated by the "RRULE" and "RDATE" properties, only one recurrenceis considered. Duplicate instances are ignored. “It is difficult to get a man to understand something, when his salary depends upon his not understanding it” -- Upton Sinclair.
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