What is Data Warehousing & why ?

qWhat is Data Warehouse?

vA centrally located database which is used to store consolidate data from different databases from different location.

vStores historical data (not transactional data) to analyze the business and  helps in creating Reports.

v As said by Bill Inmon DWH is a Subject oriented , Integrated, Non-Volatile  and Time variant Database

vData in DWH is not Normalized

vDWH is separated from Organizations operational  DBs

vData in DWH would not be refreshed Daily(should be a specific interval)

qWhy Data Warehousing is ?

vThe main purpose of a DW is to speed-up (simplify) reporting and analytic. It enables slicing and dicing of data in any way a business user can think of.

vMany big complex selects (possibly compared to few inserts, updates and deletes) that just take to long to execute (and are complicated to write)

vIf data from different systems needs to get combined