Aus dem Handbuch SC09-2508-04, Seite 257:

File description specifications identify each file used by a program. Each file in a
program must have a corresponding file description specification statement.
A file can be either program-described or externally described. In
program-described files, record and field descriptions are included within the RPG
program (using input and output specifications). Externally described files have
their record and field descriptions defined externally using DDS, DSU, IDDU, or
SQL commands. (DSU is part of the CODE/400 product.)
Möglicherweise kommt ILE aber mit dem Punkt im Namen nicht zurecht.