[From SQL Server Magazine
SQL Server 2008 has a new feature called Change Data Capture (CDC), a component of the relational database engine that provides change data for consuming applications. CDC populates change tables by asynchronously reading a given databases transaction log. CDCs most notable use is for datawarehousing apps in which you need to detect and process changed data on a recurring basis in extraction, transformation, and loading (ETL) processes. With CDC, you can detect changed data in source OLTP systems that run on SQL Server 2008 without needing to implement expensive custom solutions such as timestamps, flags, triggers, and other one-off solutions for detecting changed data.
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