The term extraction and transformation is used to describe the processes of, first, the extraction of data from source systems and, second, the modification or transformation of that same data to put it into a form that is more acceptable to the data warehouse than its native form. There are many extraction and transformation tools, and most also provide a mechanism for loading the transformed data into the warehouse. Hence, they are usually referred to as extraction, transformation, and loading (ETL) tools. In order to facilitate the loading, the ETL tool must have an understanding of the structure of the data warehouse, and so one of the components of the ETL application is a source to target mapping ...

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