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Subject: What's the difference between components
The difference between Components in iCalendnar is the conformance rules, and often conformance rules about the troika of dtStart, dtEnd, and duration, and secondarily rules about nesting. Some excerpts from RFC5545 Vevent: ; The following is REQUIRED if the component ; appears in an iCalendar object that doesn't ; specify the "METHOD" property; otherwise, it ; is OPTIONAL; in any case, it MUST NOT occur ; more than once. ; dtstart /Description: A "VEVENT" calendar component is a grouping of component properties, possibly including "VALARM" calendar components, that represents a scheduled amount of time on a calendar. For example, it can be an activity; such as a one-hour long, department meeting from 8:00 AM to 9:00 AM, tomorrow. Generally, an event will take up time on an individual calendar. Hence, the event will appear as an opaque interval in a search for busy time. Alternately, the event can have its Time Transparency set to "TRANSPARENT" in order to prevent blocking of the event in searches for busy time. The "VEVENT" is also the calendar component used to specify an anniversary or daily reminder within a calendar. These events have a DATE value type for the "DTSTART" property instead of the default value type of DATE-TIME. If such a "VEVENT" has a "DTEND" property, it MUST be specified as a DATE value also. The anniversary type of "VEVENT" can span more than one date (i.e., "DTEND" property value is set to a calendar date after the "DTSTART" property value). If such a "VEVENT" has a "DURATION" property, it MUST be specified as a "dur-day" or "dur-week" value. The "DTSTART" property for a "VEVENT" specifies the inclusive start of the event. For recurring events, it also specifies the very first instance in the recurrence set. The "DTEND" property for a "VEVENT" calendar component specifies the non-inclusive end of the event. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE value type but no "DTEND" nor "DURATION" property, the event's duration is taken to be one day. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE-TIME value type but no "DTEND" property, the event ends on the same calendar date and time of day specified by the "DTSTART" property. The "VEVENT" calendar component cannot be nested within another calendar component. However, "VEVENT" calendar components can be related to each other or to a "VTODO" or to a "VJOURNAL" calendar component with the "RELATED-TO" property. Component Name: VTODO ; The following are OPTIONAL, ; but MUST NOT occur more than once. ; class / completed / created / description / dtstart / geo / last-mod / location / organizer / percent / priority / recurid / seq / status / summary / url / ; Either 'due' or 'duration' MAY appear in ; a 'todoprop', but 'due' and 'duration' ; MUST NOT occur in the same 'todoprop'. ; If 'duration' appear in a 'todoprop', ; then 'dtstart' MUST also appear in ; the same 'todoprop'. ; due / duration /Summary: This states that the Existing vcomponents are quire specific about start/date/end and their coexistence, and not some sort of vague “any two of three”. In particular, the vtodo (and Interval started out as a profiled vtodo) is quite explicit that due and duration must not appear in the same component. If Duration exsits, then vtodo requires that dtDstart also exists. Other parts that come up, to my reading, - that vtodo allows only valarms as a subcomponents - that vevent allows only valarms as a subcomponents This has implications for the schema for intervals. tc “The single biggest problem in communication is the illusion that it has taken place.”
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