What is a data structure in COBOL?

A hierarchical organization of data items using level numbers to create logical groupings, where higher-level items contain lower-level items in a tree-like structure.

How do I create arrays and tables in COBOL?

Use the OCCURS clause to define arrays and tables. Specify the number of occurrences and optionally use INDEXED BY for efficient access using index values.

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COBOL Data Structure

Data structures organize data items hierarchically using level numbers to create logical groupings and relationships. Learn to design effective data structures with group items, elementary items, arrays, and tables.

Hierarchical Data Structure

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       WORKING-STORAGE SECTION.
       01 HIERARCHICAL-DATA-STRUCTURE.
           05 EMPLOYEE-MASTER-RECORD.              *> Level 01 - Root level
               10 EMPLOYEE-IDENTIFICATION.           *> Level 05 - Major group
                   15 EMPLOYEE-ID PIC 9(6).
                   15 EMPLOYEE-SSN PIC 9(9).
                   15 EMPLOYEE-DEPARTMENT-CODE PIC X(3).
               10 EMPLOYEE-PERSONAL-INFO.            *> Level 05 - Major group
                   15 EMPLOYEE-NAME.
                       20 EMPLOYEE-FIRST-NAME PIC X(15).
                       20 EMPLOYEE-LAST-NAME PIC X(20).
                       20 EMPLOYEE-MIDDLE-INITIAL PIC X.
                   15 EMPLOYEE-ADDRESS.
                       20 EMPLOYEE-STREET PIC X(30).
                       20 EMPLOYEE-CITY PIC X(20).
                       20 EMPLOYEE-STATE PIC X(2).
                       20 EMPLOYEE-ZIP PIC X(10).
               10 EMPLOYEE-WORK-INFO.                *> Level 05 - Major group
                   15 EMPLOYEE-POSITION PIC X(20).
                   15 EMPLOYEE-SALARY PIC 9(7)V99.
                   15 EMPLOYEE-HIRE-DATE PIC 9(8).
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-HIERARCHICAL-STRUCTURE
       
       DEMONSTRATE-HIERARCHICAL-STRUCTURE.
           MOVE 123456 TO EMPLOYEE-ID
           MOVE 123456789 TO EMPLOYEE-SSN
           MOVE 'IT' TO EMPLOYEE-DEPARTMENT-CODE
           
           MOVE 'JOHN' TO EMPLOYEE-FIRST-NAME
           MOVE 'SMITH' TO EMPLOYEE-LAST-NAME
           MOVE 'A' TO EMPLOYEE-MIDDLE-INITIAL
           
           MOVE '123 MAIN STREET' TO EMPLOYEE-STREET
           MOVE 'NEW YORK' TO EMPLOYEE-CITY
           MOVE 'NY' TO EMPLOYEE-STATE
           MOVE '10001' TO EMPLOYEE-ZIP
           
           MOVE 'SOFTWARE ENGINEER' TO EMPLOYEE-POSITION
           MOVE 75000.00 TO EMPLOYEE-SALARY
           MOVE 20230101 TO EMPLOYEE-HIRE-DATE
           
           DISPLAY 'Hierarchical Data Structure demonstration:'
           DISPLAY 'Employee ID: ' EMPLOYEE-ID
           DISPLAY 'Employee Name: ' EMPLOYEE-NAME
           DISPLAY 'Full Name: ' EMPLOYEE-FIRST-NAME ' ' EMPLOYEE-LAST-NAME
           DISPLAY 'Address: ' EMPLOYEE-ADDRESS
           DISPLAY 'Street: ' EMPLOYEE-STREET
           DISPLAY 'City: ' EMPLOYEE-CITY
           DISPLAY 'Position: ' EMPLOYEE-POSITION
           DISPLAY 'Salary: ' EMPLOYEE-SALARY.

Create hierarchical data structures using level numbers (01, 05, 10, 15, 20) to organize data in logical groups. Higher numbers represent subgroups within larger groups, creating clear data relationships.

Group Items and Elementary Items

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       WORKING-STORAGE SECTION.
       01 GROUP-AND-ELEMENTARY-ITEMS.
           05 CUSTOMER-RECORD.                      *> Group item (no PICTURE)
               10 CUSTOMER-ID PIC 9(6).             *> Elementary item
               10 CUSTOMER-NAME PIC X(30).          *> Elementary item
               10 CUSTOMER-ADDRESS.                 *> Group item (no PICTURE)
                   15 CUSTOMER-STREET PIC X(30).    *> Elementary item
                   15 CUSTOMER-CITY PIC X(20).      *> Elementary item
                   15 CUSTOMER-STATE PIC X(2).      *> Elementary item
                   15 CUSTOMER-ZIP PIC X(10).       *> Elementary item
               10 CUSTOMER-FINANCIAL-INFO.          *> Group item (no PICTURE)
                   15 CUSTOMER-BALANCE PIC 9(9)V99. *> Elementary item
                   15 CUSTOMER-CREDIT-LIMIT PIC 9(9)V99. *> Elementary item
                   15 CUSTOMER-PAYMENT-TERMS PIC X(10). *> Elementary item
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-GROUP-ELEMENTARY-ITEMS
       
       DEMONSTRATE-GROUP-ELEMENTARY-ITEMS.
           MOVE 123456 TO CUSTOMER-ID
           MOVE 'JANE DOE' TO CUSTOMER-NAME
           
           MOVE '456 OAK AVENUE' TO CUSTOMER-STREET
           MOVE 'CHICAGO' TO CUSTOMER-CITY
           MOVE 'IL' TO CUSTOMER-STATE
           MOVE '60601' TO CUSTOMER-ZIP
           
           MOVE 2500.75 TO CUSTOMER-BALANCE
           MOVE 5000.00 TO CUSTOMER-CREDIT-LIMIT
           MOVE 'NET30' TO CUSTOMER-PAYMENT-TERMS
           
           DISPLAY 'Group and Elementary Items demonstration:'
           DISPLAY 'Customer Record: ' CUSTOMER-RECORD
           DISPLAY 'Customer ID: ' CUSTOMER-ID
           DISPLAY 'Customer Name: ' CUSTOMER-NAME
           DISPLAY 'Customer Address: ' CUSTOMER-ADDRESS
           DISPLAY 'Customer Street: ' CUSTOMER-STREET
           DISPLAY 'Customer City: ' CUSTOMER-CITY
           DISPLAY 'Customer Financial Info: ' CUSTOMER-FINANCIAL-INFO
           DISPLAY 'Customer Balance: ' CUSTOMER-BALANCE
           DISPLAY 'Customer Credit Limit: ' CUSTOMER-CREDIT-LIMIT.

Group items contain other data items and have no PICTURE clause, while elementary items are the lowest level with PICTURE clauses. Use group items to organize related data and elementary items for actual data storage.

Arrays and Tables

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       WORKING-STORAGE SECTION.
       01 ARRAYS-AND-TABLES.
           05 CUSTOMER-TABLE OCCURS 100 TIMES
               INDEXED BY CUSTOMER-INDEX.
               10 CUSTOMER-TABLE-ID PIC 9(6).
               10 CUSTOMER-TABLE-NAME PIC X(30).
               10 CUSTOMER-TABLE-BALANCE PIC 9(9)V99.
           05 MONTHLY-SALES-ARRAY OCCURS 12 TIMES
               INDEXED BY MONTH-INDEX.
               10 MONTHLY-SALES-AMOUNT PIC 9(9)V99.
               10 MONTHLY-SALES-COUNT PIC 9(6).
               10 MONTHLY-SALES-DATE PIC 9(8).
           05 STATE-TAX-RATE-TABLE OCCURS 50 TIMES
               INDEXED BY STATE-INDEX.
               10 STATE-TAX-RATE-CODE PIC X(2).
               10 STATE-TAX-RATE-PERCENTAGE PIC 9(3)V99.
               10 STATE-TAX-RATE-DESCRIPTION PIC X(20).
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-ARRAYS-TABLES
       
       DEMONSTRATE-ARRAYS-TABLES.
           DISPLAY 'Arrays and Tables demonstration:'
           
           *> Initialize customer table
           MOVE 1 TO CUSTOMER-INDEX
           MOVE 123456 TO CUSTOMER-TABLE-ID(CUSTOMER-INDEX)
           MOVE 'JOHN SMITH' TO CUSTOMER-TABLE-NAME(CUSTOMER-INDEX)
           MOVE 1500.50 TO CUSTOMER-TABLE-BALANCE(CUSTOMER-INDEX)
           
           *> Initialize monthly sales array
           MOVE 1 TO MONTH-INDEX
           MOVE 25000.75 TO MONTHLY-SALES-AMOUNT(MONTH-INDEX)
           MOVE 150 TO MONTHLY-SALES-COUNT(MONTH-INDEX)
           MOVE 20230101 TO MONTHLY-SALES-DATE(MONTH-INDEX)
           
           *> Initialize state tax rate table
           MOVE 1 TO STATE-INDEX
           MOVE 'NY' TO STATE-TAX-RATE-CODE(STATE-INDEX)
           MOVE 8.25 TO STATE-TAX-RATE-PERCENTAGE(STATE-INDEX)
           MOVE 'NEW YORK STATE' TO STATE-TAX-RATE-DESCRIPTION(STATE-INDEX)
           
           DISPLAY 'Customer Table Entry:'
           DISPLAY '  ID: ' CUSTOMER-TABLE-ID(CUSTOMER-INDEX)
           DISPLAY '  Name: ' CUSTOMER-TABLE-NAME(CUSTOMER-INDEX)
           DISPLAY '  Balance: ' CUSTOMER-TABLE-BALANCE(CUSTOMER-INDEX)
           
           DISPLAY 'Monthly Sales Entry:'
           DISPLAY '  Amount: ' MONTHLY-SALES-AMOUNT(MONTH-INDEX)
           DISPLAY '  Count: ' MONTHLY-SALES-COUNT(MONTH-INDEX)
           DISPLAY '  Date: ' MONTHLY-SALES-DATE(MONTH-INDEX)
           
           DISPLAY 'State Tax Rate Entry:'
           DISPLAY '  Code: ' STATE-TAX-RATE-CODE(STATE-INDEX)
           DISPLAY '  Percentage: ' STATE-TAX-RATE-PERCENTAGE(STATE-INDEX)
           DISPLAY '  Description: ' STATE-TAX-RATE-DESCRIPTION(STATE-INDEX).

Create arrays and tables using the OCCURS clause with INDEXED BY for efficient access. Use tables for structured data storage and arrays for sequential data processing with index-based access.

Complex Data Structures

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       WORKING-STORAGE SECTION.
       01 COMPLEX-DATA-STRUCTURES.
           05 COMPANY-STRUCTURE.
               10 COMPANY-HEADER.
                   15 COMPANY-ID PIC 9(6).
                   15 COMPANY-NAME PIC X(50).
                   15 COMPANY-ADDRESS PIC X(100).
               10 DEPARTMENT-TABLE OCCURS 10 TIMES
                   INDEXED BY DEPT-INDEX.
                   15 DEPARTMENT-ID PIC X(3).
                   15 DEPARTMENT-NAME PIC X(30).
                   15 DEPARTMENT-MANAGER PIC X(30).
                   15 EMPLOYEE-TABLE OCCURS 50 TIMES
                       INDEXED BY EMP-INDEX.
                       20 EMPLOYEE-ID PIC 9(6).
                       20 EMPLOYEE-NAME PIC X(30).
                       20 EMPLOYEE-POSITION PIC X(20).
                       20 EMPLOYEE-SALARY PIC 9(7)V99.
               10 COMPANY-FINANCIAL-INFO.
                   15 TOTAL-EMPLOYEES PIC 9(4).
                   15 TOTAL-PAYROLL PIC 9(12)V99.
                   15 COMPANY-REVENUE PIC 9(12)V99.
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-COMPLEX-STRUCTURES
       
       DEMONSTRATE-COMPLEX-STRUCTURES.
           DISPLAY 'Complex Data Structures demonstration:'
           
           *> Initialize company header
           MOVE 100001 TO COMPANY-ID
           MOVE 'ACME CORPORATION' TO COMPANY-NAME
           MOVE '123 BUSINESS PARK DRIVE' TO COMPANY-ADDRESS
           
           *> Initialize first department
           MOVE 1 TO DEPT-INDEX
           MOVE 'IT' TO DEPARTMENT-ID(DEPT-INDEX)
           MOVE 'INFORMATION TECHNOLOGY' TO DEPARTMENT-NAME(DEPT-INDEX)
           MOVE 'JANE MANAGER' TO DEPARTMENT-MANAGER(DEPT-INDEX)
           
           *> Initialize first employee in IT department
           MOVE 1 TO EMP-INDEX
           MOVE 200001 TO EMPLOYEE-ID(DEPT-INDEX, EMP-INDEX)
           MOVE 'JOHN DEVELOPER' TO EMPLOYEE-NAME(DEPT-INDEX, EMP-INDEX)
           MOVE 'SOFTWARE ENGINEER' TO EMPLOYEE-POSITION(DEPT-INDEX, EMP-INDEX)
           MOVE 75000.00 TO EMPLOYEE-SALARY(DEPT-INDEX, EMP-INDEX)
           
           *> Initialize company financial info
           MOVE 1 TO TOTAL-EMPLOYEES
           MOVE 75000.00 TO TOTAL-PAYROLL
           MOVE 1000000.00 TO COMPANY-REVENUE
           
           DISPLAY 'Company Structure:'
           DISPLAY '  Company ID: ' COMPANY-ID
           DISPLAY '  Company Name: ' COMPANY-NAME
           DISPLAY '  Department: ' DEPARTMENT-NAME(DEPT-INDEX)
           DISPLAY '  Manager: ' DEPARTMENT-MANAGER(DEPT-INDEX)
           DISPLAY '  Employee: ' EMPLOYEE-NAME(DEPT-INDEX, EMP-INDEX)
           DISPLAY '  Position: ' EMPLOYEE-POSITION(DEPT-INDEX, EMP-INDEX)
           DISPLAY '  Salary: ' EMPLOYEE-SALARY(DEPT-INDEX, EMP-INDEX)
           DISPLAY '  Total Employees: ' TOTAL-EMPLOYEES
           DISPLAY '  Total Payroll: ' TOTAL-PAYROLL.

Create complex data structures with nested tables and multiple levels of organization. Use hierarchical structures to represent real-world relationships like company-department-employee structures.

Data Structure Design Principles

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       WORKING-STORAGE SECTION.
       01 DATA-STRUCTURE-DESIGN-PRINCIPLES.
           05 DESIGN-PRINCIPLES.
               10 LOGICAL-ORGANIZATION PIC X(20) VALUE 'LOGICAL'.
               10 CLEAR-HIERARCHY PIC X(20) VALUE 'HIERARCHICAL'.
               10 EFFICIENT-ACCESS PIC X(20) VALUE 'EFFICIENT'.
               10 MAINTAINABLE-DESIGN PIC X(20) VALUE 'MAINTAINABLE'.
           05 DESIGN-GUIDELINES.
               10 MEANINGFUL-NAMES PIC X(30) VALUE 'USE MEANINGFUL NAMES'.
               10 CONSISTENT-LEVELS PIC X(30) VALUE 'MAINTAIN CONSISTENT LEVELS'.
               10 APPROPRIATE-SIZES PIC X(30) VALUE 'CHOOSE APPROPRIATE SIZES'.
           05 DESIGN-BENEFITS.
               10 IMPROVED-READABILITY PIC X(30) VALUE 'IMPROVED READABILITY'.
               10 EASIER-MAINTENANCE PIC X(30) VALUE 'EASIER MAINTENANCE'.
               10 BETTER-PERFORMANCE PIC X(30) VALUE 'BETTER PERFORMANCE'.
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-DESIGN-PRINCIPLES
       
       DEMONSTRATE-DESIGN-PRINCIPLES.
           DISPLAY 'Data Structure Design Principles demonstration:'
           DISPLAY 'Design Principles:'
           DISPLAY '  Logical Organization: ' LOGICAL-ORGANIZATION
           DISPLAY '  Clear Hierarchy: ' CLEAR-HIERARCHY
           DISPLAY '  Efficient Access: ' EFFICIENT-ACCESS
           DISPLAY '  Maintainable Design: ' MAINTAINABLE-DESIGN
           DISPLAY 'Design Guidelines:'
           DISPLAY '  Names: ' MEANINGFUL-NAMES
           DISPLAY '  Levels: ' CONSISTENT-LEVELS
           DISPLAY '  Sizes: ' APPROPRIATE-SIZES
           DISPLAY 'Design Benefits:'
           DISPLAY '  Readability: ' IMPROVED-READABILITY
           DISPLAY '  Maintenance: ' EASIER-MAINTENANCE
           DISPLAY '  Performance: ' BETTER-PERFORMANCE
           
           DISPLAY 'Design Principles Summary:'
           DISPLAY '1. Organize data logically'
           DISPLAY '2. Create clear hierarchies'
           DISPLAY '3. Enable efficient access'
           DISPLAY '4. Design for maintainability'
           DISPLAY '5. Use meaningful names'
           DISPLAY '6. Maintain consistent level numbering'.

Follow design principles for effective data structures: logical organization, clear hierarchy, efficient access, maintainable design, meaningful names, and consistent level numbering for better code quality.

Data Structure Performance

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       WORKING-STORAGE SECTION.
       01 DATA-STRUCTURE-PERFORMANCE.
           05 PERFORMANCE-METRICS.
               10 ACCESS-TIME PIC 9(6).             *> Access time in microseconds
               10 MEMORY-USAGE PIC 9(8).            *> Memory usage in bytes
               10 EFFICIENCY-RATING PIC 9(3)V99.    *> Efficiency percentage
           05 OPTIMIZATION-TECHNIQUES.
               10 GROUPING-STRATEGY PIC X(20) VALUE 'LOGICAL GROUPING'.
               10 INDEXING-STRATEGY PIC X(20) VALUE 'EFFICIENT INDEXING'.
               10 MEMORY-ALIGNMENT PIC X(20) VALUE 'PROPER ALIGNMENT'.
           05 PERFORMANCE-TARGETS.
               10 TARGET-ACCESS-TIME PIC 9(6) VALUE 100.
               10 TARGET-MEMORY-USAGE PIC 9(8) VALUE 1000000.
               10 TARGET-EFFICIENCY PIC 9(3)V99 VALUE 95.00.
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-PERFORMANCE-CONSIDERATIONS
       
       DEMONSTRATE-PERFORMANCE-CONSIDERATIONS.
           DISPLAY 'Data Structure Performance demonstration:'
           
           MOVE 50 TO ACCESS-TIME
           MOVE 500000 TO MEMORY-USAGE
           COMPUTE EFFICIENCY-RATING = 92.50
           
           DISPLAY 'Performance Metrics:'
           DISPLAY '  Access Time: ' ACCESS-TIME ' microseconds'
           DISPLAY '  Memory Usage: ' MEMORY-USAGE ' bytes'
           DISPLAY '  Efficiency Rating: ' EFFICIENCY-RATING '%'
           DISPLAY 'Optimization Techniques:'
           DISPLAY '  Grouping: ' GROUPING-STRATEGY
           DISPLAY '  Indexing: ' INDEXING-STRATEGY
           DISPLAY '  Alignment: ' MEMORY-ALIGNMENT
           DISPLAY 'Performance Targets:'
           DISPLAY '  Target Access Time: ' TARGET-ACCESS-TIME ' microseconds'
           DISPLAY '  Target Memory Usage: ' TARGET-MEMORY-USAGE ' bytes'
           DISPLAY '  Target Efficiency: ' TARGET-EFFICIENCY '%'
           
           IF ACCESS-TIME <= TARGET-ACCESS-TIME
               DISPLAY 'Access time target achieved'
           END-IF
           
           IF MEMORY-USAGE <= TARGET-MEMORY-USAGE
               DISPLAY 'Memory usage target achieved'
           END-IF
           
           IF EFFICIENCY-RATING >= TARGET-EFFICIENCY
               DISPLAY 'Efficiency target achieved'
           END-IF.

Consider performance when designing data structures: optimize access time, minimize memory usage, achieve high efficiency ratings, use logical grouping, efficient indexing, and proper memory alignment.

Data Structure Best Practices

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       WORKING-STORAGE SECTION.
       01 DATA-STRUCTURE-BEST-PRACTICES.
           05 PRACTICE-GUIDELINES.
               10 CLEAR-DOCUMENTATION PIC X(30) VALUE 'CLEAR DOCUMENTATION'.
               10 CONSISTENT-NAMING PIC X(30) VALUE 'CONSISTENT NAMING'.
               10 APPROPRIATE-SIZING PIC X(30) VALUE 'APPROPRIATE SIZING'.
               10 EFFICIENT-ORGANIZATION PIC X(30) VALUE 'EFFICIENT ORGANIZATION'.
           05 IMPLEMENTATION-STANDARDS.
               10 STANDARD-LEVELS PIC X(20) VALUE 'STANDARD LEVELS'.
               10 MEANINGFUL-PREFIXES PIC X(20) VALUE 'MEANINGFUL PREFIXES'.
               10 LOGICAL-GROUPING PIC X(20) VALUE 'LOGICAL GROUPING'.
           05 MAINTENANCE-CONSIDERATIONS.
               10 EASY-MODIFICATION PIC X(30) VALUE 'EASY MODIFICATION'.
               10 CLEAR-RELATIONSHIPS PIC X(30) VALUE 'CLEAR RELATIONSHIPS'.
               10 SCALABLE-DESIGN PIC X(30) VALUE 'SCALABLE DESIGN'.
       
       PROCEDURE DIVISION.
       PERFORM DEMONSTRATE-BEST-PRACTICES
       
       DEMONSTRATE-BEST-PRACTICES.
           DISPLAY 'Data Structure Best Practices demonstration:'
           DISPLAY 'Practice Guidelines:'
           DISPLAY '  Documentation: ' CLEAR-DOCUMENTATION
           DISPLAY '  Naming: ' CONSISTENT-NAMING
           DISPLAY '  Sizing: ' APPROPRIATE-SIZING
           DISPLAY '  Organization: ' EFFICIENT-ORGANIZATION
           DISPLAY 'Implementation Standards:'
           DISPLAY '  Levels: ' STANDARD-LEVELS
           DISPLAY '  Prefixes: ' MEANINGFUL-PREFIXES
           DISPLAY '  Grouping: ' LOGICAL-GROUPING
           DISPLAY 'Maintenance Considerations:'
           DISPLAY '  Modification: ' EASY-MODIFICATION
           DISPLAY '  Relationships: ' CLEAR-RELATIONSHIPS
           DISPLAY '  Design: ' SCALABLE-DESIGN
           
           DISPLAY 'Best Practices Summary:'
           DISPLAY '1. Document data structures clearly'
           DISPLAY '2. Use consistent naming conventions'
           DISPLAY '3. Choose appropriate field sizes'
           DISPLAY '4. Organize data efficiently'
           DISPLAY '5. Use standard level numbering'
           DISPLAY '6. Design for easy maintenance'
           DISPLAY '7. Plan for future scalability'.

Follow best practices for data structures: clear documentation, consistent naming, appropriate sizing, efficient organization, standard level numbering, easy maintenance, and scalable design for long-term success.

Design hierarchical data structures with clear level relationships.
Use group items for organization and elementary items for data storage.
Create arrays and tables with OCCURS clause and INDEXED BY.
Implement complex structures with nested tables and multiple levels.
Follow design principles and best practices for maintainable code.

Data Storage

Storage formats and memory management

Data Structures

Data structures and organization