Think before you change that column

Because of the nature of the ETL life cycle, small changes can have important and not inconsequential impacts. Before you update a column’s type, or the data that it contains, or even add or remove columns you must perform Impact Analysis for the change.

This means going through and finding what relies on the data, and how it will be affected by the changes. Communication is necessary between the different parties involved in the data, generally the ETL architect, the ETL team and the source system DBA.