A data warehouse is a data store (database) which is built out of separate internal and/or external data sources where the data is integrated in a consistent manner.
The data is typically a record of an enterprise's past transactional and operational activities.
The database design favours data analysis and reporting in order to gain strategic insight and to facilitate decision making. Data warehouses are not used for current, "live" data.
Data warehouses often hold large amounts of information which are sometimes subdivided into smaller logical units called dependent data marts.
Periodically, one imports data from enterprise resource planning (ERP) systems and other related business software systems into the data warehouse for further processing. It is common practice to "stage" data prior to merging it into a data warehouse. In this sense, to "stage data" means to queue it for preprocessing, usually with an ETL tool. The preprocessing program reads the staged data (often a business's primary OLTP databases), performs qualitative preprocessing or filtering (including denormalization, if deemed necessary), and writes it into the warehouse.
Online analytical processing (OLAP) is a mode of computational analysis often used in data warehouses; conversely, online transaction processing (OLTP) is more suitable for current, normal business operations.
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