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COBOL Data Encapsulation

Data encapsulation hides internal data implementation details and provides controlled access through well-defined interfaces. Learn to implement data hiding, access control, and modular design in COBOL programs.

Basic Data Encapsulation

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       WORKING-STORAGE SECTION.
       01 CUSTOMER-DATA.
           05 CUSTOMER-ID PIC 9(6).
           05 CUSTOMER-NAME PIC X(30).
           05 CUSTOMER-BALANCE PIC 9(9)V99.
           05 CUSTOMER-STATUS PIC X.
       
       PROCEDURE DIVISION.
       *> Encapsulated data access procedures
       PERFORM INITIALIZE-CUSTOMER-DATA
       PERFORM SET-CUSTOMER-NAME USING 'JOHN SMITH'
       PERFORM GET-CUSTOMER-BALANCE INTO DISPLAY-BALANCE
       PERFORM UPDATE-CUSTOMER-STATUS USING 'A'.

Encapsulate data access through procedures rather than direct manipulation. Define procedures for initializing, setting, getting, and updating data. This provides controlled access and hides implementation details.

Data Access Procedures

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       INITIALIZE-CUSTOMER-DATA.
           MOVE 0 TO CUSTOMER-ID
           MOVE SPACES TO CUSTOMER-NAME
           MOVE 0 TO CUSTOMER-BALANCE
           MOVE 'N' TO CUSTOMER-STATUS.
       
       SET-CUSTOMER-NAME USING INPUT-NAME.
           IF FUNCTION LENGTH(FUNCTION TRIM(INPUT-NAME)) > 0
               MOVE FUNCTION UPPER-CASE(INPUT-NAME) TO CUSTOMER-NAME
               DISPLAY 'Customer name set to: ' CUSTOMER-NAME
           ELSE
               DISPLAY 'Error: Invalid customer name'
           END-IF.
       
       GET-CUSTOMER-BALANCE INTO OUTPUT-BALANCE.
           MOVE CUSTOMER-BALANCE TO OUTPUT-BALANCE
           DISPLAY 'Customer balance retrieved: ' OUTPUT-BALANCE.
       
       UPDATE-CUSTOMER-STATUS USING NEW-STATUS.
           IF NEW-STATUS = 'A' OR NEW-STATUS = 'I' OR NEW-STATUS = 'S'
               MOVE NEW-STATUS TO CUSTOMER-STATUS
               DISPLAY 'Customer status updated to: ' CUSTOMER-STATUS
           ELSE
               DISPLAY 'Error: Invalid status value: ' NEW-STATUS
           END-IF.

Create procedures for all data access operations. Include validation, error checking, and logging in access procedures. This ensures data integrity and provides a consistent interface for data manipulation.

Data Validation and Integrity

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       VALIDATE-CUSTOMER-DATA.
           MOVE 'Y' TO VALIDATION-FLAG
           
           *> Validate customer ID
           IF CUSTOMER-ID = 0 OR CUSTOMER-ID > 999999
               DISPLAY 'Error: Invalid customer ID: ' CUSTOMER-ID
               MOVE 'N' TO VALIDATION-FLAG
           END-IF.
           
           *> Validate customer name
           IF CUSTOMER-NAME = SPACES OR CUSTOMER-NAME = LOW-VALUES
               DISPLAY 'Error: Customer name is required'
               MOVE 'N' TO VALIDATION-FLAG
           END-IF.
           
           *> Validate customer balance
           IF CUSTOMER-BALANCE < 0
               DISPLAY 'Error: Customer balance cannot be negative'
               MOVE 'N' TO VALIDATION-FLAG
           END-IF.
           
           *> Validate customer status
           IF CUSTOMER-STATUS NOT = 'A' AND CUSTOMER-STATUS NOT = 'I' 
               AND CUSTOMER-STATUS NOT = 'S'
               DISPLAY 'Error: Invalid customer status: ' CUSTOMER-STATUS
               MOVE 'N' TO VALIDATION-FLAG
           END-IF.

Implement comprehensive data validation to ensure data integrity. Check all data fields for valid values, ranges, and formats. Use validation flags to track data quality and provide meaningful error messages.

Modular Data Design

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       WORKING-STORAGE SECTION.
       01 CUSTOMER-MODULE.
           05 CUSTOMER-DATA.
               10 CUSTOMER-ID PIC 9(6).
               10 CUSTOMER-NAME PIC X(30).
               10 CUSTOMER-BALANCE PIC 9(9)V99.
           05 CUSTOMER-CONTROL.
               10 VALIDATION-FLAG PIC X VALUE 'N'.
                   88 DATA-VALID VALUE 'Y'.
               10 LAST-UPDATED PIC 9(8).
               10 UPDATE-COUNT PIC 9(4) VALUE 0.
       
       01 ACCOUNT-MODULE.
           05 ACCOUNT-DATA.
               10 ACCOUNT-NUMBER PIC 9(8).
               10 ACCOUNT-TYPE PIC X.
               10 ACCOUNT-BALANCE PIC 9(9)V99.
           05 ACCOUNT-CONTROL.
               10 VALIDATION-FLAG PIC X VALUE 'N'.
                   88 DATA-VALID VALUE 'Y'.
               10 LAST-UPDATED PIC 9(8).

Design modular data structures with separate modules for different business entities. Each module contains its data and control information. This provides clear separation of concerns and easier maintenance.

Data Access Control

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       WORKING-STORAGE SECTION.
       01 ACCESS-CONTROL.
           05 USER-LEVEL PIC X.
               88 ADMIN-USER VALUE 'A'.
               88 MANAGER-USER VALUE 'M'.
               88 CLERK-USER VALUE 'C'.
           05 ACCESS-RIGHTS.
               10 CAN-READ PIC X VALUE 'N'.
               10 CAN-WRITE PIC X VALUE 'N'.
               10 CAN-DELETE PIC X VALUE 'N'.
       
       PROCEDURE DIVISION.
       PERFORM SET-ACCESS-RIGHTS
       PERFORM VALIDATE-ACCESS USING 'READ' CUSTOMER-DATA.

Implement access control to restrict data access based on user roles and permissions. Define access rights for different operations and validate access before performing data operations.

Data Hiding Techniques

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       WORKING-STORAGE SECTION.
       01 HIDDEN-DATA.
           05 INTERNAL-COUNTER PIC 9(4) VALUE 0.
           05 INTERNAL-FLAG PIC X VALUE 'N'.
           05 INTERNAL-BUFFER PIC X(100).
       
       01 PUBLIC-INTERFACE.
           05 PUBLIC-COUNTER PIC 9(4) VALUE 0.
           05 PUBLIC-STATUS PIC X VALUE 'N'.
               88 STATUS-ACTIVE VALUE 'Y'.
       
       PROCEDURE DIVISION.
       *> Only expose necessary data through public interface
       PERFORM UPDATE-PUBLIC-COUNTER USING 100
       PERFORM GET-PUBLIC-STATUS INTO DISPLAY-STATUS.

Hide internal implementation details by separating internal data from public interfaces. Only expose necessary data through well-defined public interfaces. This reduces coupling and improves maintainability.

Data Encapsulation Best Practices

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       WORKING-STORAGE SECTION.
       01 ENCAPSULATED-MODULE.
           05 MODULE-DATA.
               10 DATA-FIELD-1 PIC X(20).
               10 DATA-FIELD-2 PIC 9(6).
           05 MODULE-CONTROL.
               10 VALIDATION-FLAG PIC X VALUE 'N'.
                   88 DATA-VALID VALUE 'Y'.
               10 ERROR-COUNT PIC 9(4) VALUE 0.
           05 MODULE-INTERFACE.
               10 GET-PROCEDURE PIC X(20) VALUE 'GET-MODULE-DATA'.
               10 SET-PROCEDURE PIC X(20) VALUE 'SET-MODULE-DATA'.
               10 VALIDATE-PROCEDURE PIC X(20) VALUE 'VALIDATE-MODULE-DATA'.

Follow best practices: define clear interfaces, implement comprehensive validation, use meaningful names, group related data together, document interfaces, and maintain consistent error handling across modules.

Error Handling and Logging

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       HANDLE-DATA-ERROR USING ERROR-TYPE ERROR-MESSAGE.
           ADD 1 TO ERROR-COUNT
           DISPLAY 'Data Error: ' ERROR-TYPE ' - ' ERROR-MESSAGE
           MOVE 'N' TO VALIDATION-FLAG
           
           *> Log error for audit trail
           MOVE FUNCTION CURRENT-DATE TO ERROR-TIMESTAMP
           WRITE ERROR-LOG-RECORD
           
           *> Set appropriate return code
           IF ERROR-TYPE = 'VALIDATION'
               MOVE 4 TO RETURN-CODE
           ELSE IF ERROR-TYPE = 'ACCESS'
               MOVE 8 TO RETURN-CODE
           ELSE
               MOVE 12 TO RETURN-CODE
           END-IF.

Implement comprehensive error handling and logging for data operations. Log all errors with timestamps, set appropriate return codes, and maintain audit trails for data integrity and troubleshooting.

Data Division

Data structure and organization

Modular Programming

Modular design techniques