Data Layout in COBOL

Introduction

A layout gives detailed representation about the use of each field and the values present in it.

Data description entries

The data description entries used in COBOL are as follows:

1. Redefines Clause

To define a storage with different data description, redefines clause is used.

Syntax:

01 WS-OLD PIC X(10).
01 WS-NEW1 REDEFINES WS-OLD PIC 9(8).
01 WS-NEW2 REDEFINES WS-OLS PIC A(10).

In the above syntax, WS-OLD is redefined item and WS-NEW1 and WS-NEW2 are redefining item.

The level number should be same for redefining item and redefined item. It cannot be 66 or 88.

Example : Program to demonstrate Redefines Clause

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 WS-DESCRIPTION.
   05 WS-DATE1 VALUE '2016-07-28'.
   10 WS-YEAR PIC X(5).
   10 WS-MONTH PIC X(3).
   10 WS-DATE PIC X(2).
   05 WS-DATE2 REDEFINES WS-DATE1 PIC 9(10).

PROCEDURE DIVISION.
   DISPLAY "WS-DATE1 : "WS-DATE1.
   DISPLAY "WS-DATE2 : "WS-DATE2.

STOP RUN.

Output:
WS-DATE1 : 2016-07-28
WS-DATE2 : 2016-07-28

2. Renames Clause

This clause is used for regrouping the data names and renaming the elementary or group item.
Level number 66 is reserved for the rename clause.
Renaming is applicable only for the same level .
Level numbers 01,77, 88 or 66 are not used with the renames clause.
The renames entries should be in sequence.
Cannot rename the data items with OCCUR clause.

Example : Program to demonstrate Renames Clause

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.

DATA DIVISION.
   WORKING-STORAGE SECTION.
   01 WS-DESCRIPTION.
   05 WS-NUMBERS.
   10 WS-N1 PIC 9(2) VALUE 20.
   10 WS-N2 PIC 9(2) VALUE 56.
   10 WS-N3 PIC 9(3) VALUE 456.
   05 WS-NAMES.
   10 WS-NAME-1 PIC X(3) VALUE 'XYZ'.
   10 WS-NAME-2 PIC X(3) VALUE 'PQR'.
   10 WS-NAME-3 PIC X(3) VALUE 'ABC'.
   66 WS-RENAME RENAMES WS-N2 THRU WS-NAME-2.

PROCEDURE DIVISION.
   DISPLAY "Output of WS-RENAME : " WS-RENAME.

STOP RUN.

Output:
Output of WS-RENAME : 56456XYZPQR

3. Usage clause

This clause tells the operating system that how the data is stored internally.
Usage clause is used for every data item declared in COBOL.
This clause cannot be used in the level number 66, 77 and 88.

Following usage clauses are frequently used in COBOL:

I) DISPLAY

DISPLAY is the default usage clause.
ASCII is the memory format for storing data items. Each character in the data will take 1 byte i.e 1 digit/char =1 byte
This clause is relevant to all data types in COBOL.

II) COMP / COMPUTATIONAL

The COMP usage clause is useful only for the numeric data type.
The data item in COMP variable is stored in binary format.

Syntax:
01 NUMB PIC S9 (n) USAGE IN COMP

In above syntax, if the value of 'n' is 1 to 4, it takes 2 bytes. If the value of 'n' is 5 to 9, it takes 4 bytes. If the value of 'n' is 10 to 18, it takes 8 byte.

III) COMP-1

It is relevant to floating point data type.
In COMP-1, the data is internally stored in hexadecimal format.
Here, 1 word = 4 bytes.

IV) COMP-2

COMP-2 represents the double precision floating point number.
In COMP-2, 2 word = 8 bytes.

V) COMP-3

In COMP-3, data item is stored in a pack of decimal format.
Each digit size is 1 nibble or half byte.

4. Copybooks

In COBOL, copybook is a selection of code which defines data structure.
If the same data structure is used in many programs, then instead of writing same data structure copybook is used.
To include copybook in a program, COBOL program uses the COPY statement. This copy statement is used in a working-storage section.