In conventional as well as time-oriented databases, individual
attributes can be associated with a temporal domain, termed user-defined time. Such a domain is supported by the DBMS in
similar ways to other specialized domains, such as money, e.g., conversion to
and from a string representation and the availability of comparison predicates.
While SQL2 and DB2's SQL include two time-oriented attribute domains, datetimes and intervals, these language variants are limited to a single
calendar, the Gregorian calendar, offer little or no support for
anchored intervals,
do not support languages other than English, and exhibit many
problems with the semantics of arithmetic and boolean expressions. A
proposal is needed that addresses these problems, while providing
appropriate constructs for schema definition, time value input and output,
predicates, arithmetic manipulation, and temporal functions.