COBOL File Format

Overview

COBOL (COmmon Business-Oriented Language) is a compiled programming language designed for business, finance, and administrative systems. Developed in 1959, COBOL remains one of the most important languages in enterprise computing, particularly in mainframe environments where it processes billions of transactions daily.

Technical Details

• MIME Type: text/x-cobol
• File Extensions: .cob, .cbl, .cobol
• Category: Code
• First Appeared: 1959
• Paradigm: Procedural, imperative
• Influenced By: FLOW-MATIC, COMTRAN

Structure and Syntax

COBOL programs are organized into four main divisions with a highly structured, English-like syntax designed to be readable by business professionals.

Program Structure

       IDENTIFICATION DIVISION.
       PROGRAM-ID. HELLO-WORLD.
       AUTHOR. PROGRAMMER-NAME.
       DATE-WRITTEN. 2023-12-01.
       
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       SOURCE-COMPUTER. IBM-PC.
       OBJECT-COMPUTER. IBM-PC.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-MESSAGE PIC X(20) VALUE 'HELLO, WORLD!'.
       
       PROCEDURE DIVISION.
       MAIN-PARAGRAPH.
           DISPLAY WS-MESSAGE.
           STOP RUN.

Data Definition

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       
       01 EMPLOYEE-RECORD.
          05 EMP-ID         PIC 9(6).
          05 EMP-NAME       PIC X(30).
          05 EMP-SALARY     PIC 9(7)V99.
          05 EMP-DEPT       PIC X(10).
          05 EMP-HIRE-DATE.
             10 HIRE-YEAR   PIC 9(4).
             10 HIRE-MONTH  PIC 9(2).
             10 HIRE-DAY    PIC 9(2).
       
       01 COUNTERS.
          05 RECORD-COUNT   PIC 9(5) VALUE ZEROS.
          05 TOTAL-SALARY   PIC 9(10)V99 VALUE ZEROS.

File Processing

       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT EMPLOYEE-FILE ASSIGN TO 'EMPLOYEE.DAT'
           ORGANIZATION IS SEQUENTIAL
           ACCESS MODE IS SEQUENTIAL.
       
       DATA DIVISION.
       FILE SECTION.
       FD EMPLOYEE-FILE.
       01 EMPLOYEE-RECORD.
          05 EMP-ID      PIC 9(6).
          05 EMP-NAME    PIC X(30).
          05 EMP-SALARY  PIC 9(7)V99.
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           OPEN INPUT EMPLOYEE-FILE.
           PERFORM READ-EMPLOYEE-FILE.
           PERFORM PROCESS-RECORDS
               UNTIL END-OF-FILE.
           CLOSE EMPLOYEE-FILE.
           STOP RUN.
       
       READ-EMPLOYEE-FILE.
           READ EMPLOYEE-FILE
               AT END SET END-OF-FILE TO TRUE
           END-READ.
       
       PROCESS-RECORDS.
           IF EMP-SALARY > 50000
               DISPLAY 'HIGH EARNER: ' EMP-NAME
           END-IF.
           PERFORM READ-EMPLOYEE-FILE.

Key Features

Picture Clauses (PIC)

       01 NUMERIC-FIELDS.
          05 INTEGER-NUM     PIC 9(5).        * 5-digit integer
          05 DECIMAL-NUM     PIC 9(5)V99.     * 5.2 decimal
          05 SIGNED-NUM      PIC S9(5).       * Signed integer
          05 CURRENCY-AMT    PIC $$$,$$9.99.  * Currency format
       
       01 TEXT-FIELDS.
          05 FIXED-TEXT      PIC X(20).       * 20-character string
          05 VARIABLE-TEXT   PIC X(50) VARYING. * Variable length
          05 ALPHABETIC      PIC A(15).       * Alphabetic only

Conditional Processing

       EVALUATE EMPLOYEE-GRADE
           WHEN 'A'
               COMPUTE BONUS = SALARY * 0.15
           WHEN 'B'
               COMPUTE BONUS = SALARY * 0.10
           WHEN 'C'
               COMPUTE BONUS = SALARY * 0.05
           WHEN OTHER
               MOVE ZEROS TO BONUS
       END-EVALUATE.
       
       IF AGE >= 65
           MOVE 'ELIGIBLE' TO RETIREMENT-STATUS
       ELSE
           MOVE 'NOT-ELIGIBLE' TO RETIREMENT-STATUS
       END-IF.

Table Processing

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 SALES-TABLE.
          05 SALES-ENTRY OCCURS 12 TIMES INDEXED BY MONTH-IDX.
             10 MONTH-SALES PIC 9(8)V99.
             10 MONTH-NAME  PIC X(9).
       
       PROCEDURE DIVISION.
       LOAD-SALES-TABLE.
           PERFORM VARYING MONTH-IDX FROM 1 BY 1
               UNTIL MONTH-IDX > 12
               READ SALES-FILE INTO SALES-ENTRY(MONTH-IDX)
           END-PERFORM.
       
       CALCULATE-TOTAL-SALES.
           MOVE ZEROS TO TOTAL-SALES.
           PERFORM VARYING MONTH-IDX FROM 1 BY 1
               UNTIL MONTH-IDX > 12
               ADD MONTH-SALES(MONTH-IDX) TO TOTAL-SALES
           END-PERFORM.

Advanced Features

Database Connectivity (EXEC SQL)

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       EXEC SQL INCLUDE SQLCA END-EXEC.
       
       01 HOST-VARIABLES.
          05 H-EMP-ID     PIC 9(6).
          05 H-EMP-NAME   PIC X(30).
          05 H-EMP-SALARY PIC 9(7)V99.
       
       PROCEDURE DIVISION.
       DATABASE-OPERATIONS.
           EXEC SQL
               CONNECT TO DATABASE-NAME
           END-EXEC.
           
           EXEC SQL
               SELECT EMP_ID, EMP_NAME, EMP_SALARY
               INTO :H-EMP-ID, :H-EMP-NAME, :H-EMP-SALARY
               FROM EMPLOYEES
               WHERE EMP_ID = :H-EMP-ID
           END-EXEC.
           
           IF SQLCODE = 0
               DISPLAY 'EMPLOYEE FOUND: ' H-EMP-NAME
           END-IF.

CICS Programming

       IDENTIFICATION DIVISION.
       PROGRAM-ID. CUSTOMER-INQUIRY.
       
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 CUSTOMER-RECORD.
          05 CUST-ID      PIC 9(8).
          05 CUST-NAME    PIC X(30).
          05 CUST-BALANCE PIC S9(9)V99 COMP-3.
       
       LINKAGE SECTION.
       01 DFHCOMMAREA.
          05 COMM-CUST-ID PIC 9(8).
       
       PROCEDURE DIVISION.
       MAIN-LOGIC.
           MOVE COMM-CUST-ID TO CUST-ID.
           
           EXEC CICS READ
               DATASET('CUSTOMER')
               INTO(CUSTOMER-RECORD)
               RIDFLD(CUST-ID)
               RESP(WS-RESP)
           END-EXEC.
           
           IF WS-RESP = DFHRESP(NORMAL)
               EXEC CICS SEND MAP('CUSTMAP')
                   MAPSET('CUSTMAPS')
                   FROM(CUSTOMER-RECORD)
               END-EXEC
           END-IF.
           
           EXEC CICS RETURN END-EXEC.

Development Tools

Compilers and IDEs

• IBM Enterprise COBOL: Industry-standard compiler
• Micro Focus Visual COBOL: Modern development environment
• GnuCOBOL: Open-source COBOL compiler
• COBOL-IT: Enterprise COBOL development platform
• Eclipse COBOL: IDE plugin for COBOL development
• IBM Developer for z/OS: Mainframe development environment

Testing and Debugging

• IBM Debug Tool: Mainframe debugging
• Micro Focus Unit Test Framework: Automated testing
• COBOL Analyzer: Code analysis and metrics
• File-AID: Data manipulation and testing tool

Common Use Cases

Banking and Finance

       * Daily interest calculation
       PROCEDURE DIVISION.
       CALCULATE-DAILY-INTEREST.
           PERFORM VARYING ACCOUNT-IDX FROM 1 BY 1
               UNTIL ACCOUNT-IDX > NUMBER-OF-ACCOUNTS
               
               COMPUTE DAILY-INTEREST =
                   ACCOUNT-BALANCE(ACCOUNT-IDX) *
                   INTEREST-RATE / 365
               
               ADD DAILY-INTEREST TO
                   ACCOUNT-BALANCE(ACCOUNT-IDX)
           END-PERFORM.

Insurance Claims Processing

       * Claims validation logic
       VALIDATE-CLAIM.
           IF CLAIM-TYPE = 'AUTO'
               PERFORM VALIDATE-AUTO-CLAIM
           ELSE IF CLAIM-TYPE = 'HEALTH'
               PERFORM VALIDATE-HEALTH-CLAIM
           ELSE IF CLAIM-TYPE = 'LIFE'
               PERFORM VALIDATE-LIFE-CLAIM
           ELSE
               MOVE 'INVALID-TYPE' TO VALIDATION-STATUS
           END-IF.

Government Systems

       * Tax calculation system
       CALCULATE-TAX.
           EVALUATE TRUE
               WHEN INCOME <= 25000
                   COMPUTE TAX = INCOME * 0.10
               WHEN INCOME <= 50000
                   COMPUTE TAX = 2500 + (INCOME - 25000) * 0.15
               WHEN INCOME <= 100000
                   COMPUTE TAX = 6250 + (INCOME - 50000) * 0.25
               WHEN OTHER
                   COMPUTE TAX = 18750 + (INCOME - 100000) * 0.35
           END-EVALUATE.

Best Practices

Code Organization

• Use meaningful paragraph names
• Implement proper error handling
• Follow consistent naming conventions
• Use copybooks for common data structures
• Implement modular programming techniques

Performance Optimization

• Use COMP-3 (packed decimal) for numeric calculations
• Minimize I/O operations
• Use efficient search algorithms
• Optimize table processing with indexing

Maintenance Considerations

• Document business rules clearly
• Use structured programming techniques
• Implement proper version control
• Create comprehensive test cases

Legacy System Integration

COBOL systems often require integration with modern technologies:

• Web Services: SOAP and REST API integration
• Message Queuing: IBM MQ, Apache Kafka connectivity
• Database Access: DB2, Oracle, SQL Server integration
• Batch Processing: JCL, schedulers, and automation tools

Modern COBOL Development

Contemporary COBOL development includes:

• Object-oriented programming capabilities
• Web application development
• Cloud deployment options
• DevOps integration and continuous integration/deployment

COBOL continues to be critical in enterprise environments, processing an estimated 85% of business transactions worldwide, making it essential for maintaining and modernizing legacy systems.