Durations are a problem: XML schema types allow Years, Months, Days, Hours, Minutes, Seconds Ical allows Weeks, Days, Hours, Minutes, Seconds These overlap and we really need a combination of both. So the compromise is to have a pattern restricted String type and note that if data is to be exported into the icalendar world it cannot have years or months. Ultimately it is to be hoped the two worlds can be aligned. RFC5545 (icalendar) specifies dur-value = (["+"] / "-") "P" (dur-date / dur-time / dur-week) dur-date = dur-day [dur-time] dur-time = "T" (dur-hour / dur-minute / dur-second) dur-week = 1*DIGIT "W" dur-hour = 1*DIGIT "H" [dur-minute] dur-minute = 1*DIGIT "M" [dur-second] dur-second = 1*DIGIT "S" dur-day = 1*DIGIT "D" So P5W is valid: P5WT10M is not. If weeks re specified nothing else can be XML specifies PnYnMnDTnHnMnS The elements must appear in the order specified and the 'T' is omitted if hours minutes and seconds are absent.