Loosely speaking, the data warehouse can be defined as the decision support database that is maintained separately from the organization’s operational databases. A data warehouse is a subject oriented, integrated, time-variant and non-volatile collection of data in support of management’s decision-making process.
Features of data warehouse
A data warehouse is organized around the major subjects such as customer supplier, product, and sales, rather than concentrating on the day to day operating and transactions processing or data warehouse focuses on the modeling and analysis of data for decision makers. Hence, data warehouse typically provides s simple and concise view of particular subject issues by excluding data that are not useful in the decision support process.
A data warehouse is usually constructed by integrating multiple heterogeneous sources, such as relational databases, flat files, and online transaction, records. Data cleaning and data integration techniques are applied to ensure consistency in naming conventions.
Data are stored to provide information from on historic perspective (eg. the past 5-10 years) every key structure in the data warehouse contains, either implicitly or explicitly, a time element.
A data warehouse is always a physically separate store of data transformed from the application data found in the operational environment. Due to this separation, a data warehouse does not require transaction processing, recovery and concurrency control mechanism. It usually required only two operations in data accessing initial loading of data and access of data.