Define fields derived from existing field definitions

Listed here are the operations allowed by defining fields derived from existing field definitions.

Mapped field definitions:

Allow you to create internal fields that specify selection values, as shown in Example 7: Select records using the Open Query File (OPNQRYF) command .
Allow you to avoid confusion when the same field name occurs in multiple files, as shown in Example 1: Dynamically join database files without DDS .
Allow you to create fields that exist only in the format to be processed, but not in the database itself. This allows you to perform translate, substring, concatenation, and complex mathematical operations. The following examples describe this function.