Which statement about ETL is not correct?

a. Some estimates state that the ETL step can consume up to 80% of all efforts needed to set up a data warehouse.

b. To decrease the burden on both the operational systems and the data warehouse itself, it is recommended to start the ETL process by dumping the data in a staging area where all the ETL activities can be executed.

c. During the loading step, the data warehouse is populated by filling the fact and dimension tables, thereby also generating the necessary surrogate keys to link it all up. Fact rows should be inserted/updated before the dimension rows.

d. The extraction strategy can be either full or incremental. In the latter case, only the changes since the previous extraction are considered.