File Organization in COBOL

File organization describes how the records are organized in a file.

Types of file organization

1. Sequential file organization

A sequential file contains records used to stored and accessed in sequential order.

The key attributes of sequential file organization:
  • Records are read in sequential order. For example; It is necessary to read all previous four records to read fifth record.
  • Records are written in sequential order so that new record is always inserted at the end of the file.
  • It is not possible to delete, shorten or lengthen a record after inserting records into a sequential file.
  • The order of the record is inserted then it cannot be changed.
  • In sequential file organization, updation of record is possible. If the new record length is same as the old record length, then record can be overwritten.
Syntax for sequential organization:
INPUT-OUTPUT SECTION
FILE-CONTROL
        SELECT file-name ASSIGN TO dd-name-jcl
ORGANIZATION IS SEQUENTIAL

2. Indexed sequential file organization

An index sequential file consists of records that are accessed sequentially.

Indexed sequential file consists of two parts:
  • Data File contains the records in sequential scheme.
  • Index File contains the primary key and address of the primary key in a data file.
The key attributes of indexed sequential file organization:
  • In indexed sequential file organization, records are read sequentially similarly in sequential file organization.
  • If the primary key is known then records are accessed randomly.
  • An alternate index is generated to fetch the records.
Syntax:
INPUT-OUTPUT SECTION
FILE-CONTROL
        SELECT file-name ASSIGN TO dd-name-jcl
ORGANIZATION IS SEQUENTIAL
RECORD KEY IS primary-key
ALTERNATE RECORD KEY IS rec-key

3. Relative file organization

A relative file consists of records ordered by their relative address.

The key attributes of the relative file organization:
  • In a relative file organization, records are read sequentially similarly in the indexed sequential file organization.
  • The record is accessed by using a relative key.
  • The record is inserted using relative key and relative address is calculated using this key.
  • Relative file gives the fastest access to the records.
  • It has a disadvantage, if some intermediate records are missing, it occupies the space.
Syntax:
INPUT-OUTPUT SECTION.
FILE-CONTROL.
SELECT file-name ASSIGN TO dd-name-jcl
ORGANIZATION IS RELATIVE
RELATIVE KEY IS rec-key
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