Building the Data Warehouse

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The Evolution


The origins of DSS processing hark back to the very early days of computers and information systems. It is interesting that decision support system (DSS) processing developed out of a long and complex evolution of information technology. Its evolution continues today.


Figure 1.1 shows the evolution of information processing from the early 1960s up to 1980. In the early 1960s, the world of computation consisted of creating individual applications that were run using master files. The applications featured reports and programs, usually built in COBOL. Punched cards were common. The master files were housed on magnetic tape, which were good for storing a large volume of data cheaply, but the drawback was that they had to be accessed sequentially. In a given pass of a magnetic tape file, where 100 percent of the records have to be accessed, typically only 5 percent or fewer of the records are actually needed. In addition, accessing an entire tape file may take as long as 20 to 30 minutes, depending on the data on the file and the processing that is done.


Around the mid-1960s, the growth of master files and magnetic tape exploded. And with that growth came huge amounts of redundant data. The proliferation of master files and redundant data presented some very insidious problems:


■■ The need to synchronize data upon update ■■ The complexity of maintaining programs ■■ The complexity of developing new programs


■■ The need for extensive amounts of hardware to support all the master files


In short order, the problems of master files—problems inherent to the medium itself—became stifling.

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