Most of these systems are designed to store and retrieve data specific to the task at hand. The data is therefore transaction-oriented. And that's the way it should be. Data warehousing, on the other hand, is subject-oriented. This means that the data is structured around common business topics, allowing you to access product, account, and customer information or trends, instead of specific transactions.
Data warehousing also allows for integration of data from multiple operational sources.
Furthermore, the data stored is nonvolatile, meaning that once it has been added to the data warehouse, it never changes. These aspects of a data warehouse help make it easier to retrieve, analyze, and use information pertinent to business. Also to make timely decisions, respond quickly to competitive situations, anticipate trends, plan better, and identify areas of inefficiency. Tons of good stuff. In any case, by providing a total, or big, picture of customer activity, product trends, systems operations, etc., data warehousing can give managers a key to the future.