Extraction, Transformation, and Load (ETL)
ETL is the heart of DW.
ETL is composed of
Extraction: reading data from one or more databases,
Transformation: converting the extracted data from its previous form into the form in which it needs to be so that it can be placed into a data warehouse or simply another database, and
Load: putting the data into datawarehouse.
Transformation occurs by using rules or lookup tables or by combining the data with other data.
The three database functions are integrated into one tool to pull data out of one or more databases and place them into another, consolidated database or a data warehouse.
ETL tools transport data between sources and targets, document how data elements (e.g. metadata) change as the move between source and target, exchange metadata with other application as needed, and administer all runtime processes and operations (e.g., scheduling, error management, audit logs, statistics).