Describe field use for logical files

You can specify that the fields in logical files are to be input-only, both (input/output), or neither fields.

Do this by specifying one of the following items in position 38:
Entry
Meaning
Blank
For simple or multiple format logical files, defaults to B (both) For join logical files, defaults to I (input only).
B
Both input and output allowed; not valid for join logical files.
I
Input only (read only).
N
Neither input nor output; valid only for join logical files.
Note: The usage value (in position 38) is not used on a reference function. When another file refers to a field (using a REF or REFFLD keyword) in a logical file, the usage value is not copied into that file.