Which of the following would generally NOT be an example of a transformation performed as part of an ETL $($Extract$,$ Transform, and Load$)$ or data integration process?

Integrating data from different systems around a common key, such as a customer identification number

Aggregating data based on sales category to improve the efficiency of data warehouse queries

Obtaining data from source systems using handwritten code or with commercial data$-$integration software

Cleaning up the data by eliminating duplicate records for the same customer