A data warehouse is a repository of an organization's electronically stored data. Data warehouses are designed to facilitate reporting and analysis.
This definition of the data warehouse focuses on data storage. However, the means to retrieve and analyze data, to extract, transform and load data, and to manage the data dictionary are also considered essential components of a data warehousing system. Many references to data warehousing use this broader context. Thus, an expanded definition for data warehousing includes business intelligence tools, tools to extract, transform, and load data into the repository, and tools to manage and retrieve metadata.
Datawarehousing arises in an organisation's need for reliable, consolidated, unique and integrated reporting and analysis of its data.
The practical reality of most organisation’s is that their data infrastructure is made up by a collection of heterogeneous systems. For example, an organisation might have one system that handles customer-relationship, a system that handles employees, systems that handles sales data or production data, yet another system for finance and budgeting data etc. In practice, these systems are often poorly or not at all integrated .Another problem is that ERP systems are designed to support relevant operations.
Yet another problem might be that the organisation is, internally, in disagreement about which data is correct. For example, the sales department might have one view of its costs, while the finance department has another view of that cost. In such cases the organisation can spend unlimited time discussing who's got the correct view of the data.
It is partly the purpose of Datawarehousing to bridge such problems. It is important to note that in Datawarehousing the source ...