The two major DW gurus, Inmon and Kimball do a lot for the architecture and design of the warehouse, but, as you have noted, do little with the requirements piece.
Data Warehouse Project Management, by Adelman and Moss has a dozen or so pages on the subject.
Kimball's Lifecycle Toolkit has about 40 pages.
Both deal with interviewing end users and potential end users of the warehouse.
Basically, there are three main reasons to build a data warehouse:
- Integration of data from multiple sources.
- Reduction of processing demands on OLTP servers, or to provide a separate processing area for business analysis
- To provide a single, validated data source for corporate reporting and analysis.
Which of these three are driving your project?
Also, check out
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Sometimes the grass is greener on the other side because there is more manure there !