Cobol Data Validation

Structured COBOL Programming 10th edition

John Wiley & Sons, Inc.

Nancy Stern Hofstra University

Robert A. Stern Nassau Community College

James P. Ley University of Wisconsin-Stout PowerPoint Presentation

Winifred J. Rex Bowling Green State University

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Chapter 11

Data Validation

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Chapter Objectives To familiarize you with • Types of input errors that may occur • Techniques used to validate input data • Actions that can be taken when input errors are detected

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Chapter Contents • Avoiding Logic Errors by Validating Input • What to Do If Input Errors Occur • Global Considerations in COBOL • When Data Should Be Validated • Understanding Program Interrupts • Other Methods for Improving Program Performance 11-4

Program Errors - Syntax • Due to violations of language rules • Detected by compiler

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Program Errors - Logic • Result from using incorrect instructions or incorrect sequence of instructions • Also include run-time errors • Not detected during compilation • Found by running program with test data and comparing outcome to expected results 11-6

Avoiding Logic Errors • Develop comprehensive test data • Include all condition and types of data tested for in program • Have someone other than programmer prepare test data to avoid bias • Manually check computer-produced results for accuracy 11-7

Debugging Tips • For every IF statement, include test data that satisfies and does not satisfy condition • For multi-page report include enough test data to print several pages • Include test data that produces size errors if ON SIZE ERROR routines are used 11-8

Debugging Tips • Used DISPLAY statements during test runs to isolate logic errors • If program produces disk file, always examine it for accuracy • Check loops to see that instructions performed exact number of times required 11-9

Why Input Must Be Validated • Risk of data entry errors is high – Large volume of data entered – Human error keying in data

• Invalid input leads to inaccurate output – For example, salary reported incorrectly if entered as 23000 instead of 32000

• Input error can cause program interrupt – For example, spaces entered for numeric field used in arithmetic operation 11-10

Data Validation Techniques • Routines to identify various types of input errors • Error modules to handle each error that occurs

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Test Fields for Correct Format • Use NUMERIC class test to ensure field used in arithmetic operation has numeric value Example

If Amt-In Is Not Numeric Perform 500-Err-Rtn Else Add Amt-In To WS-Total End-If 11-12

Test Fields for Correct Format • Use ALPHABETIC class test if field must be alphabetic • Use sign test if numeric field is to have – Values greater than zero (POSITIVE) – Values less than zero (NEGATIVE) – Value equal to zero (ZERO) • S must be included in PIC to store a negative number • NOT POSITIVE is not same as NEGATIVE 11-13

Checking for missing data • Check key fields if they must contain data Example

If Soc-Sec-No = Spaces Perform 900-Err-Rtn End-If

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INSPECT Statement • Useful for validity checking as well as other purposes • Two main functions – To count number of occurrences of given character in field – To replace specific occurrences of given character with another character

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INSPECT … TALLYING • To count number of times a given character occurs Format

INSPECT identifier-1 TALLYING identifier-2 FOR ALL identifier-3 LEADING literal-1 CHARACTERS

...

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INSPECT … TALLYING • identifier-1 – Field to be "inspected"

• identifier-2 – Field where count stored – Not automatically set to zero by INSPECT

• identifier-3 or literal-1 – Character to be counted – ZERO, SPACE, 8, 'S' are valid entries for literal-1

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Options with FOR Clause • ALL - every occurrence of specified character in field counted • LEADING - all occurrences of specified character preceding any other character tallied • CHARACTERS - all characters within field tallied – Used to determine size of field 11-18

INSPECT … TALLYING Examples

Move Zeros To Ct1, Ct2, Ct3 Inspect X1 Tallying Ct1 For All Spaces Inspect X2 Tallying Ct2 For Characters Inspect X3 Tallying Ct3 For Leading Zeros

Fields

Results

X1 = bb82b X2 = AB32C X3 = 00060

Ct1 = 3 Ct2 = 5 Ct3 = 3

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BEFORE/AFTER Clause • Optional clause after FOR options to count only characters before or after some initial value Format

BEFORE AFTER

INITIAL

identifier-4 literal-2

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BEFORE/AFTER Clause Examples

Move Zeros To Ct4, Ct5 Inspect X4 Tallying Ct4 For All Zeros Before Initial 9 Inspect X5 Tallying Ct5 For Characters After Initial 6

Items

Results

X4 = 05090 X5 = 06762

Ct4 = 2 Ct5 = 3 11-21

INSPECT … REPLACING • To replace specified occurrences of a given character with another Format

INSPECT identifier-1 REPLACING CHARACTERS ALL identifier-2 BY identifier-3 LEADING literal-1 literal-2 ... FIRST 11-22

INSPECT … REPLACING • Literals must be single characters or figurative constants consistent with type of field being inspected • ALL, LEADING, CHARACTERS have same meaning as previously noted • FIRST means first occurrence of literal1 will be replaced by literal-2 • BEFORE/AFTER clause can be used 11-23

INSPECT … REPLACING Examples

Inspect Date-In Replacing All '-' By '/' Inspect SSNo Replacing All Spaces By '-' Field Date-In SSNo

Before 10-17-02 123 45 6789

After 10/17/02 123-45-6789 11-24

INSPECT … REPLACING Examples

Inspect X1 Replacing Leading 'A' By 'Z' Inspect X2 Replacing First 'R' By 'Q' Field X1 X2

Before AAABBA RRSST

After ZZZBBA QRSST 11-25

Testing for Reasonableness • Use after verifying that numeric fields contain numeric data • Range test - check that field is within established lower and upper bounds • Limit test - check that field does not exceed defined upper limit

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Checking Coded Fields • Code often stored in field to shorten record and minimize typing • For example, 'H' or 'S' may represent pay type of 'Hourly' or 'Salaried' • Use condition names to check validity of coded fields

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Checking Coded Fields Example

05 Pay-Code 88 Hourly 88 Salaried

Pic X. Value 'H'. Value 'S'.

If Hourly Or Salaried Then Perform Pay-Calc-Rtn Else Perform Pay-Code-Err-Rtn End-If

Data Division entries

Procedure Division statements 11-28

Typical Validity Checks • Class test - determine if field contains appropriate type of data (NUMERIC, ALPHABETIC) • Determine if data is missing by comparing field to SPACES • Replace spaces in numeric fields with ZEROS using INSPECT statement 11-29

Typical Validity Checks • Range test - determine if field in established range • Limit test - determine if field exceeds established limit • Determine if field contains valid codes or values using condition-names to document and test fields 11-30

EVALUATE Statement • Perform class tests first to ensure field is proper type • Use EVALUATE for further validation tests • Three common forms

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1) EVALUATE identifier EVALUATE identifier WHEN value(s) PERFORM … … Example

Evaluate Pay-Code When 'H' Perform 300-Hourly-Rtn When 'S' Perform 400-Salaried-Rtn End-Evaluate 11-32

1) EVALUATE identifier • May also use THRU clause to check range of values Example

Evaluate Age When 0 Thru 19 Perform 400-Minor-Rtn When 20 Thru 99 Perform 500-Adult-Rtn End-Evaluate

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2) EVALUATE TRUE EVALUATE TRUE WHEN condition PERFORM … … Example

Evaluate True When Age >= 0 And <= 19 Perform 400-Minor-Rtn When Age >= 20 And <= 99 Perform 500-Adult-Rtn End-Evaluate

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2) EVALUATE TRUE • Can also use with condition-names Example

Assume these condition names defined for Age field 05 Age Pic 99. 88 Minor Values 0 Thru 19. 88 Adult Values 20 Thru 99. 11-35

2) EVALUATE TRUE Evaluate True When Minor Perform 400-Minor-Rtn When Adult Perform 500-Adult-Rtn End-Evaluate

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2) EVALUATE TRUE • Note that using Age in place of True in this statement causes syntax error • Must compare numeric field Age to another numeric field or numeric literal • Compare TRUE to a condition or condition-name with value of TRUE or FALSE

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3) EVALUATE condition EVALUATE condition WHEN TRUE PERFORM … WHEN FALSE PERFORM … Example

Evaluate Age <= 19 When True Perform 400-Minor-Rtn When False Perform 500-Adult-Rtn End-Evaluate 11-38

Actions If Input Errors Occur 1. Print error record displaying key field, field in error and error message 2. Stop the run to preserve data integrity 3. Partially process or bypass erroneous records 4. Stop the run if number of errors exceeds predetermined limit 11-39

Actions If Input Errors Occur 5. Use switch or field to indicate when record contains error – Initialize field to 'N' for no errors – Set field to 'Y' anytime an error occurs – Process record as valid only if switch field still 'N' after all validation checks

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Actions If Input Errors Occur 1. Print count totals and compare to manual counts – Print count of all records processed – Print count of all errors encountered – Print batch totals or count of all records within specific groups or batches

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Global Considerations • Meaning of comma and decimal point in numbers in United States is reversed in some other nations • 4,123.45 in United States represented as 4.123,45 in other nations • To change representation of numbers in COBOL use SPECIAL-NAMES paragraph 11-42

SPECIAL-NAMES paragraph Environment Division. Configuration Section. Special-Names. Decimal-Point is Comma. • Number 4123,45 stored in field with PIC 9999V99 • When moved to report-item with PIC 9.999,99 is displayed as 4.123,45

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COBOL 2002+ Changes • Restrictions on INSPECT statement limiting AFTER/BEFORE items to onecharacter literals or fields in REPLACING clause will be eleiminated • VALIDATE statement introduced to check format of data field

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Program Interrupts • Termination of program caused by logic error • List of common program interrupts and their causes follows

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Common Program Interrupts • Data Exception – Performing one of these operations on field containing blanks or other nonnumeric characters • Arithmetic operation • Comparison

– Failing to initialize subscript or index

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Common Program Interrupts • Divide Exception – Attempting to divide by zero

• Addressing Error – Referring to array or table entry with value in subscript or index that exceeds number of entries in table – Improperly coding nested PERFORMs or exiting from paragraph being performed 11-47

Common Program Interrupts • Operation Error – Attempting to access file with READ or WRITE before opening it or after closing it

• Specification Error – Attempting to access input area after AT END condition

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Common Program Interrupts • Illegal Character in Numeric Field – May be caused by type mismatch between actual data and PIC clause – Field size specified in PIC clause may not match actual size of field in record, leading to invalid (nonnumeric) characters from another field being treated as part of numeric field

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Chapter Summary • Two types of program errors – Syntax errors – Logic errors

• Error control procedures can minimize errors but not eliminate them entirely

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Chapter Summary • Types of error control procedures – Range tests – Limit tests – Format tests – Tests for missing data – Sequence checks

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Chapter Summary • Other methods to validate data – INSPECT statement – Condition-names – EVALUATE verb – Verifying input data

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Chapter Summary • Handling input errors – Stop the run – Fill erroneous fields with spaces or zeros – Stop the run if number of errors excessive – Print control listings or audit trails to be checked

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Copyright © 2003 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.

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