To define a relative file with a record length of 80 characters:
file-control.
select relfil
assign to "relfil.dat"
organization is relative
access mode is random
relative key is relfil-key.
file section.
fd relfil
record contains 80 characters.
01 recseq-fd-record pic x(80).
...
working-storage section.
01 relfil-key pic 9(8) comp-x.
The record key is relfil-key. When you are randomly accessing this file, there is no KEY IS field on the READ statement, the number in relfil-key determines which record is read. For sequential access, a simple READ NEXT statement gets the next record.