A general classification structure. The classification may be time stamped. The class which is be used to classify the parent element. The naming system within which the class is defined and unique. The date that the classification became valid. The date and time that the classification became valid. The date that the classification became invalid. The date and time that the classification became invalid. A comment about the classification. This type disallows an "empty" dateTime value. This type should not be used directly except to derive another type. All date types should be derived from this type rather than using xsd:date. A date in the gregorian calendar.