Extract, transform, load (ETL)
is a process separated into three functions which is used in maintaining databases, particularly in data warehousing. The first process extracts the data from a specified database, after it reads the data to determine the desired subset of data. The transform function then converts that subset of data to the desired state, which may result from creating combinations with other data, typically for purposes of storing it in the proper format or structure for querying and/or analysis. Lastly, the load function writes the transformed data to a target database, which may be a data mart, operational data store or data warehouse.”
In contrast to ETL – extract, load, transform (ELT) is a process in which raw data is transferred to a data warehouse on a target server, where the information is prepared for downstream uses.