File description specifications identify
each file used by a module or procedure. 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.)
The following limitations apply:
Only one primary file can be specified. It must be specified as a global
file. The presence of a primary file is not required.
Only one record-address file is a allowed in a module; it must be defined
as a global file.
A maximum of eight PRINTER files is allowed for global files defined in
the main source section, and a maximum of eight local PRINTER files is allowed
in each procedure.
There is no limit for the maximum number of files allowed.
Local files defined in subprocedures must be full-procedural files.
Files defined in subprocedures do not have Input and Output specifications,
so all input and output must be done using data structures.