COBOL has support to 3 principle file
organizations :
- Sequential
organization - Relative
organization (Random organization or Direct Access) - Indexed
Sequential organization
All these three organizations can be used on DISK
files; only the SEQUENTIAL organization can be used with TAPE files.
All files must be declared in the ENVIRONMENT
division by proper SELECT statements which should contain a phrase describing
to the compiler what type of organization the file should have. A second
important declaration should be placed in the FILE-SECTION where the programmer
desrcibes the record format associated to the file in FD blocks.
Finally, the PROCEDURE division should have
proper OPEN/CLOSE and READ/WRITE etc. statements used in compliance with the
logic (algorithm) of the program.
