What a data warehouse is not
By Bill Inmon
Some topics just never seem to die, however much their demise is deserved. When you think you have heard the last of something, here it comes again, just like a bad penny.
Recently, I was at a conference, and I heard the following discussion about what a data warehouse was. One person suggested that a data warehouse was really all the old legacy systems connected by software that could access the data. By calling such a contraption a data warehouse, the organization could avoid having to do the hard and complex work of integration.
There are so many problems with this federated approach to a data warehouse that they are almost not worth repeating here. But (once again!) here goes.
A federated data warehouse:
- Has terrible performance problems,
- Has no integration of data,
- Has no reliable source of historical data,
- Requires the cooperation of Armonk, Larry Ellison and Bill Gates, among others,
- Has no repeatability of processing, and so forth.
A federated data warehouse is no data warehouse at all.
Another person suggested that a data mart was a data warehouse. In this case, it was suggested that an organization build a data mart for finance. Then, the data mart could be expanded with new requirements for marketing. Then sales could add on, and so forth.
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