What are the main file organizations in COBOL?

Main file organizations in COBOL include sequential files, indexed files, relative files, and VSAM files, each optimized for different access patterns and performance requirements.

How do you read files in COBOL?

Files in COBOL are read using READ statements with appropriate access methods, file status checking, and record processing techniques for different file organizations.

What is record processing in COBOL?

Record processing in COBOL involves handling individual records within files, including record layout definition, data validation, and record manipulation operations.

How do you handle file errors in COBOL?

File errors in COBOL are handled using file status codes, exception handling routines, and error recovery procedures to manage various file operation failures.

What are file access methods in COBOL?

File access methods in COBOL include sequential access, random access, dynamic access, and skip sequential access, each providing different performance characteristics.

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COBOL File Processing Concepts

File processing in COBOL involves reading, writing, and manipulating data files using various file organizations, access methods, and record handling techniques. Understanding file processing concepts is fundamental to COBOL programming as most business applications require efficient data file management. Proper file processing ensures data integrity, performance optimization, and reliable data operations.

Understanding File Processing

File processing in COBOL encompasses all methods of handling data files including file definition, record processing, data validation, and file operations. Different file organizations and access methods provide various performance characteristics and capabilities. Understanding these concepts is essential for choosing the right file processing approach for specific business requirements.

File Organizations

1. Sequential Files

Sequential files store records in the order they are written, providing simple and efficient processing for applications that process all records in order. This organization is ideal for batch processing and report generation.

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       DATA DIVISION.
       FILE SECTION.
       FD INPUT-FILE.
       01 INPUT-RECORD.
           05 CUSTOMER-ID       PIC 9(5).
           05 CUSTOMER-NAME     PIC X(20).
           05 CUSTOMER-BALANCE  PIC 9(8)V99.
       
       FD OUTPUT-FILE.
       01 OUTPUT-RECORD.
           05 REPORT-LINE       PIC X(80).
       
       WORKING-STORAGE SECTION.
       01 FILE-CONTROLS.
           05 INPUT-STATUS      PIC XX VALUE '00'.
           05 OUTPUT-STATUS     PIC XX VALUE '00'.
               88 FILE-OK       VALUE '00'.
               88 FILE-EOF      VALUE '10'.
       
       PROCEDURE DIVISION.
       PROCESS-SEQUENTIAL-FILE.
           DISPLAY 'Processing sequential file'
           
           OPEN INPUT INPUT-FILE
           OPEN OUTPUT OUTPUT-FILE
           
           PERFORM UNTIL FILE-EOF
               READ INPUT-FILE
               IF FILE-OK
                   PERFORM PROCESS-RECORD
               END-IF
           END-PERFORM
           
           CLOSE INPUT-FILE
           CLOSE OUTPUT-FILE.
       
       PROCESS-RECORD.
           DISPLAY 'Processing record: ' CUSTOMER-ID ' ' CUSTOMER-NAME
           STRING CUSTOMER-ID DELIMITED BY SIZE
                  ' ' DELIMITED BY SIZE
                  CUSTOMER-NAME DELIMITED BY SIZE
                  ' Balance: ' DELIMITED BY SIZE
                  CUSTOMER-BALANCE DELIMITED BY SIZE
                  INTO REPORT-LINE
           END-STRING
           WRITE OUTPUT-RECORD

Sequential file processing reads records in the order they appear in the file. This approach is efficient for batch processing where all records need to be processed in sequence.

2. Indexed Files

Indexed files provide both sequential and random access capabilities using key fields. This organization allows efficient retrieval of specific records and supports complex data relationships.

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       DATA DIVISION.
       FILE SECTION.
       FD CUSTOMER-FILE.
       01 CUSTOMER-RECORD.
           05 CUSTOMER-ID       PIC 9(5).
           05 CUSTOMER-NAME     PIC X(20).
           05 CUSTOMER-ADDRESS  PIC X(50).
           05 CUSTOMER-BALANCE  PIC 9(8)V99.
       
       WORKING-STORAGE SECTION.
       01 FILE-CONTROLS.
           05 FILE-STATUS       PIC XX VALUE '00'.
               88 FILE-OK       VALUE '00'.
               88 FILE-EOF      VALUE '10'.
               88 RECORD-FOUND  VALUE '00'.
               88 RECORD-NOT-FOUND VALUE '23'.
       
       PROCEDURE DIVISION.
       PROCESS-INDEXED-FILE.
           DISPLAY 'Processing indexed file'
           
           OPEN I-O CUSTOMER-FILE
           
           *> Random access by customer ID
           MOVE 12345 TO CUSTOMER-ID
           READ CUSTOMER-FILE
           IF RECORD-FOUND
               DISPLAY 'Found customer: ' CUSTOMER-NAME
               PERFORM UPDATE-CUSTOMER-BALANCE
           ELSE
               DISPLAY 'Customer not found: ' CUSTOMER-ID
           END-IF
           
           CLOSE CUSTOMER-FILE.
       
       UPDATE-CUSTOMER-BALANCE.
           ADD 100.00 TO CUSTOMER-BALANCE
           REWRITE CUSTOMER-RECORD

Indexed files provide efficient random access to records using key fields. This allows programs to quickly locate and update specific records without reading the entire file.

Record Processing

1. Record Layout Definition

Record layout definition specifies the structure and format of records within files. Proper record definition ensures data integrity and efficient processing.

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       DATA DIVISION.
       FILE SECTION.
       FD EMPLOYEE-FILE.
       01 EMPLOYEE-RECORD.
           05 EMPLOYEE-ID       PIC 9(6).
           05 EMPLOYEE-NAME.
               10 FIRST-NAME     PIC X(15).
               10 LAST-NAME      PIC X(20).
           05 EMPLOYEE-ADDRESS.
               10 STREET         PIC X(30).
               10 CITY           PIC X(20).
               10 STATE          PIC X(2).
               10 ZIP-CODE       PIC X(10).
           05 EMPLOYEE-DATA.
               10 HIRE-DATE      PIC 9(8).
               10 SALARY         PIC 9(8)V99.
               10 DEPARTMENT     PIC X(10).
       
       WORKING-STORAGE SECTION.
       01 RECORD-COUNTERS.
           05 TOTAL-RECORDS     PIC 9(6) VALUE 0.
           05 VALID-RECORDS     PIC 9(6) VALUE 0.
           05 INVALID-RECORDS   PIC 9(6) VALUE 0.
       
       PROCEDURE DIVISION.
       PROCESS-RECORDS.
           DISPLAY 'Processing employee records'
           
           PERFORM UNTIL FILE-EOF
               READ EMPLOYEE-FILE
               IF FILE-OK
                   ADD 1 TO TOTAL-RECORDS
                   PERFORM VALIDATE-RECORD
                   IF RECORD-VALID
                       ADD 1 TO VALID-RECORDS
                       PERFORM PROCESS-VALID-RECORD
                   ELSE
                       ADD 1 TO INVALID-RECORDS
                       PERFORM PROCESS-INVALID-RECORD
                   END-IF
               END-IF
           END-PERFORM

Record layout definition provides a clear structure for data within files. Hierarchical record structures help organize related data fields logically.

2. Record Validation

Record validation ensures data integrity by checking record content for correctness, completeness, and business rule compliance before processing.

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       PROCEDURE DIVISION.
       VALIDATE-RECORD.
           MOVE 'VALID' TO RECORD-STATUS
           
           *> Check required fields
           IF EMPLOYEE-ID = 0
               DISPLAY 'ERROR: Employee ID is required'
               MOVE 'INVALID' TO RECORD-STATUS
           END-IF
           
           IF FIRST-NAME = SPACES
               DISPLAY 'ERROR: First name is required'
               MOVE 'INVALID' TO RECORD-STATUS
           END-IF
           
           IF LAST-NAME = SPACES
               DISPLAY 'ERROR: Last name is required'
               MOVE 'INVALID' TO RECORD-STATUS
           END-IF
           
           *> Check data ranges
           IF SALARY < 0 OR SALARY > 999999.99
               DISPLAY 'ERROR: Salary out of range: ' SALARY
               MOVE 'INVALID' TO RECORD-STATUS
           END-IF
           
           *> Check date format
           IF HIRE-DATE NOT NUMERIC
               DISPLAY 'ERROR: Invalid hire date: ' HIRE-DATE
               MOVE 'INVALID' TO RECORD-STATUS
           END-IF.
       
       PROCESS-VALID-RECORD.
           DISPLAY 'Processing valid record: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME.
       
       PROCESS-INVALID-RECORD.
           DISPLAY 'Skipping invalid record: ' EMPLOYEE-ID

Record validation ensures data quality by checking required fields, data ranges, and format compliance. Invalid records are identified and handled appropriately.

File Access Methods

1. Sequential Access

Sequential access reads records in the order they appear in the file, providing efficient processing for applications that need to process all records.

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       PROCEDURE DIVISION.
       SEQUENTIAL-ACCESS.
           DISPLAY 'Using sequential access'
           
           OPEN INPUT INPUT-FILE
           
           PERFORM UNTIL FILE-EOF
               READ INPUT-FILE
               IF FILE-OK
                   PERFORM PROCESS-CURRENT-RECORD
               END-IF
           END-PERFORM
           
           CLOSE INPUT-FILE.
       
       PROCESS-CURRENT-RECORD.
           DISPLAY 'Processing record: ' RECORD-NUMBER
           ADD 1 TO RECORD-NUMBER
           
           *> Process record data
           PERFORM CALCULATE-TOTALS
           PERFORM UPDATE-STATISTICS

Sequential access is the most efficient method for processing all records in a file. It provides optimal performance for batch processing applications.

2. Random Access

Random access allows direct retrieval of specific records using key values, providing efficient access to individual records without reading the entire file.

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       PROCEDURE DIVISION.
       RANDOM-ACCESS.
           DISPLAY 'Using random access'
           
           OPEN INPUT CUSTOMER-FILE
           
           *> Read specific customer by ID
           MOVE 12345 TO CUSTOMER-ID
           READ CUSTOMER-FILE
           IF RECORD-FOUND
               DISPLAY 'Found customer: ' CUSTOMER-NAME
               PERFORM PROCESS-CUSTOMER
           ELSE
               DISPLAY 'Customer not found: ' CUSTOMER-ID
           END-IF
           
           *> Read another customer
           MOVE 67890 TO CUSTOMER-ID
           READ CUSTOMER-FILE
           IF RECORD-FOUND
               DISPLAY 'Found customer: ' CUSTOMER-NAME
               PERFORM PROCESS-CUSTOMER
           ELSE
               DISPLAY 'Customer not found: ' CUSTOMER-ID
           END-IF
           
           CLOSE CUSTOMER-FILE.
       
       PROCESS-CUSTOMER.
           DISPLAY 'Processing customer: ' CUSTOMER-ID ' ' CUSTOMER-NAME

Random access provides efficient retrieval of specific records using key values. This method is ideal for applications that need to access individual records quickly.

File Error Handling

1. File Status Checking

File status checking monitors file operations for errors and exceptional conditions, providing detailed information about operation results.

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       PROCEDURE DIVISION.
       FILE-OPERATIONS-WITH-STATUS.
           DISPLAY 'Performing file operations with status checking'
           
           OPEN INPUT INPUT-FILE
           IF NOT FILE-OK
               DISPLAY 'ERROR: Cannot open input file. Status: ' FILE-STATUS
               PERFORM FILE-ERROR-HANDLING
               STOP RUN
           END-IF
           
           PERFORM UNTIL FILE-EOF
               READ INPUT-FILE
               EVALUATE FILE-STATUS
                   WHEN '00'
                       PERFORM PROCESS-RECORD
                   WHEN '10'
                       DISPLAY 'End of file reached'
                   WHEN '23'
                       DISPLAY 'ERROR: Record not found'
                   WHEN '24'
                       DISPLAY 'ERROR: File locked'
                   WHEN OTHER
                       DISPLAY 'ERROR: File operation failed. Status: ' FILE-STATUS
                       PERFORM FILE-ERROR-HANDLING
               END-EVALUATE
           END-PERFORM
           
           CLOSE INPUT-FILE.
       
       FILE-ERROR-HANDLING.
           DISPLAY 'Handling file error with status: ' FILE-STATUS
           ADD 1 TO ERROR-COUNT

File status checking provides detailed information about file operation results. Different status codes indicate various conditions including success, end-of-file, and error conditions.

2. Error Recovery Procedures

Error recovery procedures handle file errors gracefully, providing retry mechanisms, fallback procedures, and clean error handling for various failure conditions.

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       PROCEDURE DIVISION.
       ERROR-RECOVERY.
           DISPLAY 'Implementing error recovery procedures'
           
           PERFORM FILE-OPERATION-WITH-RETRY
           ON EXCEPTION
               DISPLAY 'File operation failed, attempting recovery'
               PERFORM RECOVERY-PROCEDURES
           END-PERFORM.
       
       FILE-OPERATION-WITH-RETRY.
           PERFORM VARYING RETRY-COUNT FROM 1 BY 1
               UNTIL RETRY-COUNT > 3
               PERFORM ATTEMPT-FILE-OPERATION
               IF FILE-OK
                   EXIT PERFORM
               ELSE
                   DISPLAY 'Retry attempt ' RETRY-COUNT ' failed'
                   PERFORM WAIT-BEFORE-RETRY
               END-IF
           END-PERFORM.
       
       RECOVERY-PROCEDURES.
           DISPLAY 'Executing recovery procedures'
           PERFORM CLEANUP-RESOURCES
           PERFORM LOG-ERROR-DETAILS
           PERFORM NOTIFY-ADMINISTRATOR

Error recovery procedures provide retry mechanisms and fallback procedures for handling file errors. These procedures help maintain program stability and provide graceful error handling.

Best Practices for File Processing

Choose Appropriate Organization: Select file organization based on access patterns and performance requirements
Validate Records: Always validate record data before processing
Check File Status: Monitor file status codes for all file operations
Handle Errors Gracefully: Implement proper error handling and recovery procedures
Optimize Access Patterns: Use appropriate access methods for different operations
Document File Layouts: Document record layouts and file structures clearly

Common File Processing Patterns

Batch Processing: Use sequential access for processing all records
Random Retrieval: Use indexed files for quick record access
Data Validation: Implement comprehensive record validation
Error Handling: Provide robust error handling and recovery
Performance Optimization: Choose appropriate file organizations and access methods
Data Integrity: Ensure data consistency and integrity in file operations

COBOL File Processing Concepts

Understanding File Processing

File Organizations

1. Sequential Files

2. Indexed Files

Record Processing

1. Record Layout Definition

2. Record Validation

File Access Methods

1. Sequential Access

2. Random Access

File Error Handling

1. File Status Checking

2. Error Recovery Procedures

Best Practices for File Processing

Common File Processing Patterns

File Handling

File Operations

Record Management

Indexed Files

File Status

Data Management