And unnecessary for data warehouse processing. The source of nearly all data warehouse data is the operational environment. It is a temptation to think that there is massive redundancy of data between the two environments. Indeed, the first impression many people draw is that of great redundancy of data between the operational environment and the data warehouse environment. Such an understanding is superficial and demonstrates a lack of understanding as to what is occurring in the data warehouse.
Much data never passes out of the operational environment.
Only that data that is needed for DSS processing finds its way into the data warehouse environment. Data in the operational environment is very fresh. Data in the warehouse is much older. From the perspective of time horizons alone, there is very little overlap between the operational and the data warehouse environments. Figure 3 illustrates that most data is significantly altered upon being selected for and moving into the data warehouse.