文档介绍：More Consideration to Time in Data Warehouses
Qi LI, Yingcai BAI
Dept. puter Sci. And Eng. , A9803023# Shanghai Jiaotong Univ. ,
Shanghai 200030, China
E-mail: happylq@
Abstract granularities, and more over, these query may be
Time plays an important role in data based on a calendar different from Gregorian calendar,
warehouse(DW), the Gregorian calendar such as financial year, which begins at this March to
(consists of day, month and year)monly next year March. In addition, the data dumping and
used as time dimension in DW. While in many view maintenance are often set to take place
situations, a calendar closely related to the periodically in DW, which are triggered at an
operation of the business is also needed. particularly point of time that is closely related to the
However, current SQL language doesn’t support business behavior, for example, the data dumping is
the definition of time granularity and calendar executed in the seventh day after each financial month,
efficiently from the view of DW. how to formally and systematically define these
Based on a general framework for time triggers need a well-defined time system. So a well-
granularity, we propose two CREATE clauses to defined and anized time system which not
define time granularity and calendar respectively. only supports multiple time granularities but also
And to facilitate th