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The Art of SQL by Peter Robson, Stephane Faroult

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Data Warehousing

The purpose of this book is not to devote half a chapter to covering the complex issues linked to data warehousing . Many books on the topic of data warehousing have been written, some of them generic (Ralph Kimball's The Data Warehouse Toolkit and Bill Inmon's Building the Data Warehouse , both published by John Wiley & Sons, are probably the two best-known titles), some of them specific to a DBMS engine. There has been something of a religious war between the followers of Inmon, who advocates a clean 3NF design of enormous data repositories used by decision-support systems, and the supporters of Kimball, who believes that data warehouses are a different world with different needs, and that therefore the 3NF model, in spite of its qualities in the operational world, is better replaced with dimensional modeling , in which reference data is happily denormalized.

As most of this book advocates and assumes a clean 3NF design, I will deal hereafter more specifically with dimensional models, to study their strengths and the reason for their popularity, but also their weaknesses. I will, in particular, examine the interactions between operational data stores ("production databases " to the less enlightened) and decision-support systems, since data doesn't fall from heaven, unless you are working for NASA or a satellite operating company, and what you load into dimensional models has to come from somewhere. Understand that it is not because one is using the SQL language ...

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