Loading_the_Data_Warehouse - LOADING DATA INTO THE...

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L OADING D ATA I NTO T HE W AREHOUSE BY W. H. Inmon
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L O A D I N G D A T A I N T O T H E W A R E H O U S E ©Copyright 2000 by William H. Inmon, all rights reserved Page 1 The data warehouse is loaded with data that has been transformed coming from operational systems. The data coming from the operational systems undergoes a significant amount of conversion and transformation before the data is readied for loading into the data warehouse. This transformation and conversion is a complex subject that has been documented and discussed widely in the trade press, books, articles, white papers, and other places. This white paper is on the mechanics and techniques required for the movement of data from the operational environment to the data warehouse environment. Figure 1 shows the subject for conversation. There is one universal underlying assumption made about the movement of data from the operational environment to the data warehouse environment and that assumption is that if operational data must be repeatedly scanned and rescanned prior to refreshment into the data warehouse environment that the resources required for such an approach are prohibitive. One of the hallmarks of good interface design between the operational and data warehouse environment is that each operational unit of data be scanned once in its life as to possible entry and transport to the data warehouse environment. T HREE T YPES O F L OADS There are three types of loads into the data warehouse that the designer must concern himself/herself with: the loading of data already archived, the loading of data contained in existing applications, the trapping of ongoing changes to the operational environment from the last time data was loaded into the data warehouse.
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L O A D I N G D A T A I N T O T H E W A R E H O U S E ©Copyright 2000 by William H. Inmon, all rights reserved Page 2 Figure 2 shows the three types of loads. Each of these types of loads has its own special set of considerations. L OADING A RCHIVAL D ATA The simplest type of load is that of loading older existing archival data into the data warehouse. Figure 3 illustrates this type of load.
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L O A D I N G D A T A I N T O T H E W A R E H O U S E ©Copyright 2000 by William H. Inmon, all rights reserved Page 3 Archival data is usually stored on some form of sequential bulk storage. The data is read from the bulk storage and transformed into data ready to go into the warehouse. The same transformation of data occurs here as for other types of loads. Occasionally the metadata is lost for the older archival data. Under anything but the most unusual of circumstances, the inability to relate archival data to its metadata renders the archival data useless. Many companies have such undisciplined control of their archival data or such little use for the archival data that the archival data is not loaded into the data warehouse. In any case, when such a load occurs, the load is done only once. Because of its infrequent
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