User-defined time is an uninterpreted attribute domain of date
and time. User-defined time is parallel to domains such as ``money''
and integer—unlike transaction time and valid time, it has no
special query language support. It may be used for attributes such as
``birth day'' and ``hiring date.''
Conventional database management systems generally support a time
and/or date attribute domain. The SQL2 standard has explicit support
for user-defined time in its datetime and interval types.