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COBOL Indexed Files Concepts

Indexed files in COBOL provide efficient data access through the use of indexes that map key values to record locations. This file organization allows both sequential and random access patterns, making it ideal for applications requiring fast key-based record retrieval. Understanding indexed file concepts is essential for building high-performance COBOL applications that need efficient data access and management.

Understanding Indexed Files

Indexed files in COBOL use indexes to provide efficient access to records based on key values. The index contains key values and their corresponding record locations, allowing fast random access and maintaining sorted order. Indexed files support primary keys for unique identification and alternate keys for additional access paths. This organization provides excellent performance for both sequential and random access patterns.

Indexed File Definition

1. Basic Indexed File Structure

Indexed files are defined using the INDEXED clause in the SELECT statement, with primary and alternate keys specified in the record description. This structure provides the foundation for efficient key-based access.

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. INDEXED-FILE-EXAMPLE.
       
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT CUSTOMER-FILE ASSIGN TO 'CUSTOMER.DAT'
               ORGANIZATION IS INDEXED
               ACCESS MODE IS DYNAMIC
               RECORD KEY IS CUSTOMER-ID
               ALTERNATE RECORD KEY IS CUSTOMER-NAME
               WITH DUPLICATES
               FILE STATUS IS FILE-STATUS.
       
       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.
           05 CUSTOMER-PHONE    PIC X(12).
       
       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.
       MAIN-PROGRAM.
           DISPLAY 'Indexed File Example'
           PERFORM OPEN-FILE
           PERFORM DEMONSTRATE-ACCESS-METHODS
           PERFORM CLOSE-FILE
           STOP RUN.

Indexed files are defined with ORGANIZATION IS INDEXED and specify primary and alternate keys. The ACCESS MODE determines how the file can be accessed, and DUPLICATES allows multiple records with the same alternate key.

2. Key Definition and Management

Key definition involves specifying primary keys for unique record identification and alternate keys for additional access paths. Proper key design is crucial for optimal performance and data integrity.

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       DATA DIVISION.
       FILE SECTION.
       FD EMPLOYEE-FILE.
       01 EMPLOYEE-RECORD.
           05 EMPLOYEE-ID       PIC 9(6).           *> Primary key
           05 EMPLOYEE-NAME.
               10 FIRST-NAME     PIC X(15).
               10 LAST-NAME      PIC X(20).
           05 EMPLOYEE-DATA.
               10 DEPARTMENT     PIC X(10).         *> Alternate key
               10 SALARY         PIC 9(8)V99.
               10 HIRE-DATE      PIC 9(8).
           05 EMPLOYEE-ADDRESS.
               10 STREET         PIC X(30).
               10 CITY           PIC X(20).
               10 STATE          PIC X(2).
               10 ZIP-CODE       PIC X(10).
       
       WORKING-STORAGE SECTION.
       01 KEY-MANAGEMENT.
           05 PRIMARY-KEY       PIC 9(6).
           05 ALTERNATE-KEY     PIC X(10).
           05 KEY-STATUS        PIC X(1).
               88 KEY-VALID     VALUE 'V'.
               88 KEY-INVALID   VALUE 'I'.
       
       PROCEDURE DIVISION.
       KEY-OPERATIONS.
           DISPLAY 'Managing indexed file keys'
           
           *> Set primary key for random access
           MOVE 123456 TO PRIMARY-KEY
           PERFORM ACCESS-BY-PRIMARY-KEY
           
           *> Set alternate key for department search
           MOVE 'SALES' TO ALTERNATE-KEY
           PERFORM ACCESS-BY-ALTERNATE-KEY.
       
       ACCESS-BY-PRIMARY-KEY.
           MOVE PRIMARY-KEY TO EMPLOYEE-ID
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               DISPLAY 'Found employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
           ELSE
               DISPLAY 'Employee not found: ' EMPLOYEE-ID
           END-IF.

Key management involves using primary keys for unique record access and alternate keys for additional search criteria. Proper key usage ensures efficient data retrieval and maintains data integrity.

Access Methods

1. Sequential Access

Sequential access reads records in key order, providing efficient processing when all records need to be processed in sorted sequence. This method is ideal for batch processing and report generation.

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       PROCEDURE DIVISION.
       SEQUENTIAL-ACCESS.
           DISPLAY 'Sequential access to indexed file'
           
           OPEN INPUT EMPLOYEE-FILE
           
           *> Read records in key order
           PERFORM UNTIL FILE-EOF
               READ EMPLOYEE-FILE NEXT
               IF FILE-OK
                   PERFORM PROCESS-EMPLOYEE-RECORD
               END-IF
           END-PERFORM
           
           CLOSE EMPLOYEE-FILE.
       
       PROCESS-EMPLOYEE-RECORD.
           DISPLAY 'Processing employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
           ADD 1 TO RECORD-COUNT
           
           *> Process employee data
           PERFORM CALCULATE-SALARY-STATISTICS
           PERFORM UPDATE-DEPARTMENT-TOTALS

Sequential access using READ NEXT processes records in key order, providing efficient batch processing capabilities. This method is optimal when all records need to be processed in sequence.

2. Random Access

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

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       PROCEDURE DIVISION.
       RANDOM-ACCESS.
           DISPLAY 'Random access to indexed file'
           
           OPEN I-O EMPLOYEE-FILE
           
           *> Access specific employee by ID
           MOVE 123456 TO EMPLOYEE-ID
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               DISPLAY 'Found employee: ' FIRST-NAME ' ' LAST-NAME
               PERFORM UPDATE-EMPLOYEE-SALARY
           ELSE
               DISPLAY 'Employee not found: ' EMPLOYEE-ID
           END-IF
           
           *> Access another employee
           MOVE 789012 TO EMPLOYEE-ID
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               DISPLAY 'Found employee: ' FIRST-NAME ' ' LAST-NAME
               PERFORM DISPLAY-EMPLOYEE-DETAILS
           ELSE
               DISPLAY 'Employee not found: ' EMPLOYEE-ID
           END-IF
           
           CLOSE EMPLOYEE-FILE.
       
       UPDATE-EMPLOYEE-SALARY.
           ADD 5000.00 TO SALARY
           REWRITE EMPLOYEE-RECORD

Random access provides direct record retrieval using key values, enabling fast updates and individual record processing without sequential file traversal.

3. Dynamic Access

Dynamic access combines sequential and random access capabilities, allowing programs to switch between access methods as needed. This provides maximum flexibility for complex data processing.

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       PROCEDURE DIVISION.
       DYNAMIC-ACCESS.
           DISPLAY 'Dynamic access to indexed file'
           
           OPEN I-O EMPLOYEE-FILE
           
           *> Start at specific key position
           MOVE 100000 TO EMPLOYEE-ID
           START EMPLOYEE-FILE KEY IS GREATER THAN EMPLOYEE-ID
           
           *> Read sequentially from that position
           PERFORM UNTIL FILE-EOF
               READ EMPLOYEE-FILE NEXT
               IF FILE-OK
                   IF SALARY > 50000.00
                       PERFORM PROCESS-HIGH-SALARY-EMPLOYEE
                   ELSE
                       PERFORM PROCESS-STANDARD-EMPLOYEE
                   END-IF
               END-IF
           END-PERFORM
           
           CLOSE EMPLOYEE-FILE.
       
       PROCESS-HIGH-SALARY-EMPLOYEE.
           DISPLAY 'High salary employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
           ADD 1 TO HIGH-SALARY-COUNT.
       
       PROCESS-STANDARD-EMPLOYEE.
           DISPLAY 'Standard employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
           ADD 1 TO STANDARD-EMPLOYEE-COUNT

Dynamic access provides flexibility by allowing programs to start at specific positions and switch between sequential and random access as needed for complex processing requirements.

Key Management

1. Duplicate Key Handling

Duplicate key handling manages situations where multiple records have the same key value, providing control over record ordering and access patterns.

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       PROCEDURE DIVISION.
       DUPLICATE-KEY-HANDLING.
           DISPLAY 'Handling duplicate keys'
           
           OPEN INPUT EMPLOYEE-FILE
           
           *> Access by alternate key (department)
           MOVE 'SALES' TO DEPARTMENT
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               DISPLAY 'First sales employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
               
               *> Read additional records with same key
               PERFORM UNTIL FILE-EOF
                   READ EMPLOYEE-FILE NEXT
                   IF FILE-OK
                       IF DEPARTMENT = 'SALES'
                           DISPLAY 'Sales employee: ' EMPLOYEE-ID ' ' FIRST-NAME ' ' LAST-NAME
                           ADD 1 TO SALES-COUNT
                       ELSE
                           EXIT PERFORM
                       END-IF
                   END-IF
               END-PERFORM
           ELSE
               DISPLAY 'No sales employees found'
           END-IF
           
           CLOSE EMPLOYEE-FILE.
       
       DISPLAY-SALES-STATISTICS.
           DISPLAY 'Total sales employees: ' SALES-COUNT

Duplicate key handling allows multiple records with the same alternate key value. Programs can access all records with the same key using sequential reads after the initial key-based access.

2. Key Validation

Key validation ensures that key values are valid before attempting file operations, preventing errors and ensuring data integrity in indexed file operations.

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       PROCEDURE DIVISION.
       KEY-VALIDATION.
           DISPLAY 'Validating keys before file operations'
           
           *> Validate primary key
           MOVE INPUT-EMPLOYEE-ID TO EMPLOYEE-ID
           PERFORM VALIDATE-PRIMARY-KEY
           
           IF KEY-VALID
               READ EMPLOYEE-FILE
               IF RECORD-FOUND
                   PERFORM PROCESS-EMPLOYEE
               ELSE
                   DISPLAY 'Employee not found: ' EMPLOYEE-ID
               END-IF
           ELSE
               DISPLAY 'Invalid employee ID: ' INPUT-EMPLOYEE-ID
           END-IF.
       
       VALIDATE-PRIMARY-KEY.
           MOVE 'V' TO KEY-STATUS
           
           *> Check for valid range
           IF EMPLOYEE-ID < 100000 OR EMPLOYEE-ID > 999999
               DISPLAY 'ERROR: Employee ID out of range: ' EMPLOYEE-ID
               MOVE 'I' TO KEY-STATUS
           END-IF
           
           *> Check for numeric
           IF EMPLOYEE-ID NOT NUMERIC
               DISPLAY 'ERROR: Employee ID must be numeric: ' EMPLOYEE-ID
               MOVE 'I' TO KEY-STATUS
           END-IF

Key validation ensures that key values meet required criteria before file operations. This prevents errors and maintains data integrity in indexed file processing.

Performance Optimization

1. Index Optimization

Index optimization involves choosing appropriate keys, minimizing index size, and optimizing access patterns to achieve optimal performance for indexed file operations.

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       PROCEDURE DIVISION.
       INDEX-OPTIMIZATION.
           DISPLAY 'Optimizing index performance'
           
           *> Use most selective key first
           PERFORM ACCESS-BY-MOST-SELECTIVE-KEY
           
           *> Minimize index updates
           PERFORM BATCH-UPDATE-OPERATIONS
           
           *> Use appropriate access mode
           PERFORM CHOOSE-OPTIMAL-ACCESS-MODE.
       
       ACCESS-BY-MOST-SELECTIVE-KEY.
           *> Use primary key for unique access
           MOVE UNIQUE-EMPLOYEE-ID TO EMPLOYEE-ID
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               DISPLAY 'Found unique employee: ' EMPLOYEE-ID
           END-IF.
       
       BATCH-UPDATE-OPERATIONS.
           DISPLAY 'Performing batch updates'
           *> Group similar operations to minimize index updates
           PERFORM VARYING UPDATE-INDEX FROM 1 BY 1
               UNTIL UPDATE-INDEX > 10
               PERFORM SINGLE-UPDATE-OPERATION
           END-PERFORM

Index optimization focuses on using the most selective keys, minimizing index updates, and choosing appropriate access modes to achieve optimal performance for indexed file operations.

2. Access Pattern Optimization

Access pattern optimization involves choosing the most efficient access method for specific operations, minimizing I/O operations, and optimizing data retrieval patterns.

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       PROCEDURE DIVISION.
       ACCESS-PATTERN-OPTIMIZATION.
           DISPLAY 'Optimizing access patterns'
           
           *> Use random access for individual records
           PERFORM RANDOM-ACCESS-FOR-SINGLE-RECORDS
           
           *> Use sequential access for batch processing
           PERFORM SEQUENTIAL-ACCESS-FOR-BATCH-PROCESSING
           
           *> Use dynamic access for complex queries
           PERFORM DYNAMIC-ACCESS-FOR-COMPLEX-QUERIES.
       
       RANDOM-ACCESS-FOR-SINGLE-RECORDS.
           MOVE SPECIFIC-EMPLOYEE-ID TO EMPLOYEE-ID
           READ EMPLOYEE-FILE
           IF RECORD-FOUND
               PERFORM PROCESS-SINGLE-EMPLOYEE
           END-IF.
       
       SEQUENTIAL-ACCESS-FOR-BATCH-PROCESSING.
           PERFORM UNTIL FILE-EOF
               READ EMPLOYEE-FILE NEXT
               IF FILE-OK
                   PERFORM PROCESS-EMPLOYEE-FOR-BATCH
               END-IF
           END-PERFORM

Access pattern optimization involves choosing the most efficient access method for specific operations, balancing performance requirements with processing needs.

Best Practices for Indexed Files

Common Indexed File Patterns

File Processing

Learn file processing

File Operations

Master file operations

Search Techniques

Learn search techniques

Data Management

Master data management

File Status

Learn file status handling

Performance Tuning

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