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A data warehouse is a central repository for all or significant parts of the data that an enterprise's various business systems collect. The term was coined by Bill Inmon. IBM sometimes uses the term "information warehouse."

 Bill Inmon, known as the father of Data Warehousing, defines Data Warehouse as follows:


            “A data warehouse is a subject oriented, integrated, time-variant, non-volatile    


            collection of data in support of management decisions.” 

            The   passenger   reservation   systems (PRS) is an OLTP system characterized  by  large  numbers  of  concurrent  reservation users actively  adding  and  modifying  data. As the online PRS generates increasing volume of data, the need to analyze data is becoming more and more by higher management for  (i) managing and utilizing the existing   resources   and   (ii) creating   new resources for the convenience   of   passengers.  However, when Railway management wants to analyze the data, a myriad of problems often prohibit the data from being used: 

  •   Railway managers (even the Railway Programmers) cannot generate ad hoc queries.
  •   Application   Database   is segmented across multiple servers throughout the country making it difficult for the Railway users to find the data in the first place.
  •   Database Administrators prohibit ad-hoc querying of PRS OLTP systems, to prevent analytical users from running queries (e.g. how many passengers are booked for a given journey Day) as these slow down the performance of mission-critical PRS databases.