A Data Warehouse is a collection of datasets originating from one or several transaction systems (also known as registration systems) gathered to combine these into useful management information.
Due to its American origin, the process of setting up a Data Warehouse has been turned into a gerund-like word called data warehousing.
The term was introduced by William H. Inmon in 1990 which he defined as follows:
A data warehouse is a subject-oriented, integrated, nonvolatile, time-variant collection of data in support of management's decisions.
While Inmon pioneered the area of decision support and data warehousing, Ralph Kimball was the one that laid down a solid theoretical foundation for building data warehouses. Many practical aspects were tackled in his writings in a clear and accessible way. A respected American Data Warehousing consultant stated it like this:
Kimball is an expert when it comes to understanding and documenting star schema design and working with the business users. He has created the concept of slowly changing dimensions of reporting - as is versus as was - and has solved every technical issue that has ever been presented to him and those he has discovered on his own. His strength lies in implementation.
In the last few years there has been a remarkable shift. Activities which formed part of a Data Warehouse project, are now regarded as steps belonging to a Business Intelligence initiative. Kimball writes the following in Eight Guidelines for Low-Risk Enterprise Data Warehousing
A few years ago, data warehousing was relabeled as “business intelligence.” This relabeling was far more than a marketing tactic because it correctly signaled the transfer of the initiative and ownership of the data assets to the business users. Everyone knows instinctively that they can do a better job if they can see the right data. Our job in IT is to sort through all the technology in order to give the users what they want.
In short, the term data warehouse was demoted to signify only the underlying datastructure meant for numerous Business Intelligence reporting tools to acquire information from. A good functional and technical design of a data warehouse is fundamental for eg. the level of detail, the mutual relations and the performance by which information can be retrieved.
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