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 |
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 |
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