Date and Time Formats - (W3C Note as of 2002-08-20) defines a profile of ISO 8601 that is restricted but likely to satisfy most requirements
Date and Time on the Internet: Timestamps - (IETF RFC 3339) defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar, Chris Newman and Graham Klyne, July 2002