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.
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.
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.
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
|