A properly designed data warehouse improves data quality and consistency. A separate data warehouse eliminates much of the contention for resources between operational and informational systems. Data are extracted from various databases. Data are transformed and integrated before loading into the warehouse. The data warehouse is a read-only database with detailed and summary data.
Users access the data warehouse through query languages and analytical tools.
A typical three level architecture adds data marts to the generic architecture. The data marts are subsets of the data warehouse, designed to meet the decision-making needs of a specific set of users. EDW and Data Mart server different purposes and have different data structures. Transforming data is two-step process. Data marts are customized for each set of users.