While I was on a sales call yesterday I found myself explaining away what a data warehouse is. Honestly I was in some way caught off guard by the question. I shouldn't have been but I guess I haven't had to do such in a while. Or maybe I thought that data warehousing has been around for "so long" I presumed everybody would somehow know about it. This is undoubtedly a bad assumption on my part.
Nonetheless it was a refreshing surprise. It is not exactly easy to answer the question of what is a data warehouse. I wanted to be "accurate" and provide a portrayal that is both "textbook" and draws from my own account over the years.
I believe the essence of a data warehouse is data consistency and non-volatility. A data warehouse is an integration of information gathered from different operational applications and other data sources used to support business analysis activities and decision-making tasks. It captures an organization’s past transactional and operational information and changes. The data in the warehouse, in most cases, is read-only. Unlike OLTP systems, the architecture (and the technologies) of a data warehouse is optimized to favor efficient data analysis and reporting.
I suppose my view of a data warehouse, in many ways, aligns with Inmon’s top-down approach. But that certainly does not preclude me from also seeing it as a collection of more subject-oriented data marts – Kimball’s bottom-up approach.