Final answer:
The ETL process characteristic that requires source data to be altered and standardized for a data warehouse is data integration. This process ensures uniformity in format and context for combined data from various sources.
Step-by-step explanation:
The characteristic that requires the ETL process (Extract, Transform, Load) to alter or transform the source data into a standardized representation before loading it into the data warehouse is data integration. This process ensures that data from different sources is brought together and made uniform in format, scale, and context, thereby creating a consolidated dataset within the data warehouse.
Data cleansing is another essential aspect of ETL that involves rectifying or removing incorrect, corrupted, or irrelevant data. However, it is the data integration aspect that specifically deals with transforming and standardizing data to achieve a unified format suitable for a data warehouse.