You can introduce data from a flat file to a mapping using a flat file operator. You can use a flat file operator either as a source or a target. There are differences in code generation languages for flat file sources and targets.
As a source, the flat file operator acts as the row set generator that reads from a flat file using the SQL*Loader utility. A mapping with a flat file target generates a PL/SQL package that loads data into a flat file instead of loading data into rows in a table.
You can locate the Flat File Operator in the Mapping Editor (highlighted in the screenshot).
When you use a flat file operator, Warehouse Builder generates SQL*Loader code. In cases where large volumes of data are to be extracted and little transformation is required, you can use the flat file operator.
From the flat file operator, you could load data to a staging table, add indexes, and perform transformations as necessary. The transformations that you can perform on data introduced by a flat file operator are limited to SQL*Loader transformations only.