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1. Extracting

Extracting the data from different sources – the data sources can be files (like CSV, JSON, XML) or RDBMS etc.

2. Transforming

Transforming the data – this may involve cleaning, filtering, validating and applying business rules.

Cleaning (e.g. “Male” to “M” and “Female” to “F” etc.)
Filtering (e.g. selecting only certain columns to load)
Enriching (e.g. Full name to First Name , Middle Name , Last Name)
Splitting a column into multiple columns and vice versa
Joining together data from multiple sources

3. Loading

Loading – data is loaded into a data warehouse or any other database or application that houses data.

References:

http://blog.appliedinformaticsinc.com/etl-extract-transform-and-load-process-concept/