XQuery

The Duration Types

XQuery uses three types to represent durations of time: xs:duration, xs:yearMonthDuration, and xs:dayTimeDuration.

The xs:duration type represents a duration of time expressed as a number of years, months, days, hours, minutes, and seconds. Its format is PnYnMnDTnHnMnS, where P is a literal value that starts the expression, nY is the number of years followed by a literal Y, and so on where M refers to months, D refers to days, H refers to hours, the second M refers to minutes, and S refers to seconds. T is a literal value that separates the date and time. The numbers are all integers, except the number of seconds, which may be a decimal number. It is also possible to have a negative duration by preceding the P with a minus sign (−).

The xs:duration type is not totally ordered, meaning that values of this type cannot always be compared. For example, if you try to determine whether the xs:duration value P1M is greater than or less than the xs:duration value P30D, it is ambiguous. Months may have 28, 29, 30, or 31 days. So, is 30 days less than a month, or not?

The yearMonthDuration and dayTimeDuration Types

Because xs:duration is not ordered, XQuery defines two types that are derived from duration: xs:yearMonthDuration and xs:dayTimeDuration. By ensuring that month and day components never appear in the same duration, the ambiguity is eliminated.

Values of type xs:yearMonthDuration can only specify years and months, and they are represented as PnYnM. Values ...