Day 16: COBOL Indexed File Handling for Fast Record Access and Efficient Data Updates

 

1. Introduction: Moving from Sequential to Indexed File Organization

In earlier lessons, we worked with sequential files, where data had to be processed one record at a time from start to end. While simple, sequential access becomes inefficient when files grow large — especially if you need to locate or update specific records quickly.

This is where indexed file handling comes in.
Indexed files allow direct access to any record using a key field (like Employee ID or Account Number). This means COBOL can locate, read, or modify a single record without scanning the entire file.

Think of it like a small built-in database — the index acts like a catalog that keeps track of record positions for fast lookups. This approach made COBOL extremely powerful for business systems such as banking, payroll, and retail, where performance and accuracy are crucial.

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2. Creating and Using Indexed Files in COBOL

To work with indexed files, we define a KEY field in the FILE SECTION and specify that the file is ORGANIZATION IS INDEXED.

Here’s a complete example that demonstrates how to create, read, and update records in an indexed file.

Program: Indexed Employee File Handling

IDENTIFICATION DIVISION.
PROGRAM-ID. INDEXEMP.

ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL.
    SELECT EMPFILE ASSIGN TO "EMPINDEX.DAT"
        ORGANIZATION IS INDEXED
        ACCESS MODE IS DYNAMIC
        RECORD KEY IS EMP-ID
        FILE STATUS IS WS-FILE-STATUS.

DATA DIVISION.
FILE SECTION.
FD  EMPFILE.
01  EMP-RECORD.
    05 EMP-ID        PIC 9(4).
    05 EMP-NAME      PIC A(20).
    05 EMP-SALARY    PIC 9(6)V99.

WORKING-STORAGE SECTION.
01  WS-FILE-STATUS   PIC XX.
01  WS-CHOICE        PIC 9 VALUE 1.
01  WS-SEARCH-ID     PIC 9(4).

PROCEDURE DIVISION.
    DISPLAY "CREATING EMPLOYEE INDEXED FILE..."
    OPEN OUTPUT EMPFILE
    MOVE 1001 TO EMP-ID
    MOVE "ALICE" TO EMP-NAME
    MOVE 50000 TO EMP-SALARY
    WRITE EMP-RECORD
    MOVE 1002 TO EMP-ID
    MOVE "BOB" TO EMP-NAME
    MOVE 45000 TO EMP-SALARY
    WRITE EMP-RECORD
    CLOSE EMPFILE

    DISPLAY "READING SPECIFIC RECORD..."
    OPEN I-O EMPFILE
    MOVE 1002 TO EMP-ID
    READ EMPFILE KEY IS EMP-ID
        INVALID KEY DISPLAY "RECORD NOT FOUND"
        NOT INVALID KEY DISPLAY "FOUND: " EMP-NAME " $" EMP-SALARY
    END-READ

    DISPLAY "UPDATING RECORD..."
    MOVE 1002 TO EMP-ID
    READ EMPFILE KEY IS EMP-ID
        INVALID KEY DISPLAY "RECORD NOT FOUND"
        NOT INVALID KEY
            MOVE 47000 TO EMP-SALARY
            REWRITE EMP-RECORD
            DISPLAY "RECORD UPDATED SUCCESSFULLY"
    END-READ

    CLOSE EMPFILE
    DISPLAY "PROGRAM COMPLETE."
STOP RUN.

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Explanation:

• ORGANIZATION IS INDEXED – Defines the file as an indexed file.

• RECORD KEY IS EMP-ID – Identifies the field used for indexing.

• ACCESS MODE IS DYNAMIC – Allows both sequential and random access.

• READ ... KEY IS EMP-ID – Retrieves the record with the specified key.

• REWRITE – Updates the current record in the file.

• FILE STATUS – Stores success or error codes after file operations.

Indexed file handling allows you to add, retrieve, or update records instantly using a unique key — similar to how a database uses primary keys.

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3. Practical Use Cases and Best Practices

Common Business Scenarios:

• 🔹 Employee Management Systems: Retrieve or modify data by employee ID.

• 🔹 Banking Applications: Access specific account numbers quickly.

• 🔹 Inventory Management: Update product details using product codes.

Best Practices:

• Always include FILE STATUS to detect errors and avoid crashes.

• Keep key fields unique to prevent data duplication.

• Use ACCESS MODE IS DYNAMIC for flexible record handling.

• Always CLOSE the file properly after read or update operations.

• Avoid unnecessary REWRITE operations to maintain file integrity.

Indexed files make COBOL a data management powerhouse, enabling fast and precise record manipulation even with large datasets — a reason COBOL still powers critical legacy systems worldwide.

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🧠 Key Takeaways

• Indexed files allow direct access using KEY fields.

• Use ORGANIZATION IS INDEXED and RECORD KEY to define them.

• READ ... KEY IS and REWRITE let you modify specific records.

• FILE STATUS helps track file operation results.

• Indexed organization enables database-like efficiency in COBOL programs.

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💻 Practice Task

1. Create a program STUINDEX.cbl that:

   • Stores student records (Roll No, Name, Grade) in an indexed file STUFILE.DAT.

   • Allows the user to search for a specific roll number and display details.

2. Add functionality to update a student’s grade using the REWRITE statement.

3. Bonus: Implement a feature to delete a record using DELETE and confirm it’s removed.

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