File Access Modes in COBOL

COBOL an acronym for Common Business Oriented Language is a computer programming language, which was designed for business use. In COBOL, file access modes are used to specify how to access data from various file organizations according to requirements. In COBOL, there are 3 types of file organization:

• Sequential: Records that are stored and accessed in sequential order.
• Indexed: Records that can be accessed both directly and sequentially.
• Relative: Records are arranged according to their relative addresses.

Different file access modes can be used to access the data within the file for each file organization scheme. The following are the various access modes provided by COBOL:

• Sequential Access
• Random Access
• Dynamic Access

The below table shows the file organizations and the access modes of files:

File organization	Order of records	Access mode
Sequential	Order in which they were inserted	Sequential Access
Indexed	Based on the value of the record key	Sequential, Random, Dynamic Access
Relative	Order of relative record number	Sequential, Random Dynamic Access

Sequential Access:

The file’s records can be accessed from top to bottom, or sequentially from the beginning of the file towards its end.

• Records in sequential files can be retrieved in the order they were initially inserted.
• For indexed files, the record key values are the parameters used to retrieve the records.
• Relative record keys are used to retrieve records from relative files.

Cobol

IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS SEQUENTIAL
    ACCESS MODE IS SEQUENTIAL


IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS INDEXED
    ACCESS MODE IS SEQUENTIAL
    RECORD KEY IS GFG-KEY1


IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS RELATIVE
    ACCESS MODE IS SEQUENTIAL
    RELATIVE KEY IS GFG-KEY1

Random Access:

By providing the key value, records can be accessed randomly from any point in the file. Only Indexed and Relative files can be used in this mode.

• For indexed files, records are retrieved in accordance with the key field value.
• Records are retrieved for relative files in accordance with the value specified in the relative key.

Cobol

IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS INDEXED
    ACCESS MODE IS RANDOM
    RECORD KEY IS GFG-KEY1


IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS RELATIVE
    ACCESS MODE IS SEQUENTIAL
    RELATIVE KEY IS GFG-KEY1

Dynamic Access:

The records can be accessed both randomly and sequentially; for instance, we can use one file definition to obtain some records by providing the key values and some records by providing the key values in sequential order.

• Records in sequential files can be retrieved by going from top to bottom.
• Records can be obtained sequentially or randomly for relative and index files.

Cobol

IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
    FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS SEQUENTIAL
    ACCESS MODE IS DYNAMIC
    RECORD KEY IS GFG-KEY1


IDENTIFICATION DIVISION.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
    FILE-CONTROL.
    SELECT GFGFILE1 ASSIGN TO DISK
    ORGANIZATION IS RELATIVE
    ACCESS MODE IS SEQUENTIAL
    RELATIVE KEY IS GFG-KEY1