data warehouse is used for to store the large volumes of
data.it can be used for future forecasting.it is the
collection of key pieces of information that can be used for
to take the dession by the managers.

The main aim of data warehouse is in analyzing the large
volumes of data so that it can be helpful in taking business
decisions

for reporting one day details also enough.but analysis 
means we need comparision means we need some old data is 
called historical data.the data ware house saves historical 
data ,we con't to any data base manuplations.


where is in normal databases we arte able to maintain some 
extent of data .after that for entering new data u need to 
delete the old data.

BUT in Data ware house u are able to stote years of records 
no need to delete the old data