A copy of the data in a database, created specifically to allow users to query the database. Creating a data warehouse allows you to structure the data for easiest reporting and for best security–for example, pre-joining tables to assist with queries by novice users, or removing fields that contain sensitive data. It also lets you move the data to another server to minimize the performance impact that queries can cause. Because data in a data warehouse is a snapshot of a database, it must be refreshed periodically; the exact interval depends on your application needs.