What Is a Data Warehouse?

At its core, a data warehouse is a collection of data designed for the easy extraction of information. It can be in any form, including a series of text files, but most often it is a relational database. Because of this, most developers think of a data warehouse simply as a reporting database. And although that is not the most highbrow definition,it is fairly accurate.

Many developers will have differing opinions on what is the best way to design a data warehouse. But there
are common characteristics you can expect to see in all of them. The first common characteristic is a set of values used for reports. These are called measures. For example, InventoryUnits and SalesDollars can be considered measures. Another common characteristic found in data warehouses is a set of dimensions. Dimensions describe the measured data. Examples of dimensions include the dates that the InventoryUnits were documented or the zip code of the customers who bought a particular product.

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Another define of Data Warehouse

A data warehouse is a system that retrieves
and consolidates data periodically from the source systems into a dimensional or normalized
data store. It usually keeps years of history and is queried for business intelligence or other analytical
activities. It is typically updated in batches, not every time a transaction happens in the
source system.

By: Designing a Data Warehouse