cobol data validation
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11-1
Structured COBOL Programming
Nancy Stern Hofstra University
Robert A. Stern Nassau Community College
James P. Ley University of Wisconsin-Stout
John Wiley & Sons, Inc.
PowerPoint Winifred J. Rex Presentation Bowling Green State University
10th edition
11-2
Data Validation
Chapter 11
11-3
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
11-4
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
11-5
Program Errors - Syntax
• Due to violations of language rules
• Detected by compiler
11-6
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
11-7
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
11-8
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
11-9
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
11-10
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
11-11
Data Validation Techniques
• Routines to identify various types of input errors
• Error modules to handle each error that occurs
11-12
Test Fields for Correct Format
• Use NUMERIC class test to ensure field used in arithmetic operation has numeric value
If Amt-In Is Not NumericPerform 500-Err-RtnElse
Add Amt-In To WS-Total
End-If
Example
11-13
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
11-14
Checking for missing data
• Check key fields if they must contain data
If Soc-Sec-No = Spaces
Perform 900-Err-Rtn
End-If
Example
11-15
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
INSPECT identifier-1 TALLYING
identifier-2 FOR ALL identifier-3
LEADING literal-1 ...
CHARACTERS
Format
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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
11-18
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
11-19
INSPECT … TALLYING
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 Ct1 = 3
X2 = AB32C Ct2 = 5
X3 = 00060 Ct3 = 3
Examples
11-20
BEFORE/AFTER Clause
• Optional clause after FOR options to count only characters before or after some initial value
BEFORE INITIAL identifier-4
AFTER literal-2
Format
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BEFORE/AFTER Clause
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 Ct4 = 2
X5 = 06762 Ct5 = 3
Examples
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INSPECT … REPLACING
• To replace specified occurrences of a given character with another
INSPECT identifier-1 REPLACING
CHARACTERS
ALL identifier-2 BY identifier-3
LEADING literal-1 literal-2 ...
FIRST
Format
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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 literal-1 will be replaced by literal-2
• BEFORE/AFTER clause can be used
11-24
INSPECT … REPLACING
Inspect Date-In Replacing All '-' By '/'
Inspect SSNo Replacing All Spaces By '-'
Field Before After
Date-In 10-17-02 10/17/02
SSNo 123 45 6789 123-45-6789
Examples
11-25
INSPECT … REPLACING
Inspect X1 Replacing Leading 'A' By 'Z'
Inspect X2 Replacing First 'R' By 'Q'
Field Before After
X1 AAABBA ZZZBBA
X2 RRSST QRSST
Examples
11-26
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
11-27
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
11-28
Checking Coded Fields
05 Pay-Code Pic X.
88 Hourly Value 'H'.
88 Salaried Value 'S'.
If Hourly Or Salaried Then
Perform Pay-Calc-Rtn
Else
Perform Pay-Code-Err-Rtn
End-If
Example
Data Division entries
Procedure Division statements
11-29
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
11-30
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
11-31
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 ……
Evaluate Pay-Code
When 'H' Perform 300-Hourly-Rtn
When 'S' Perform 400-Salaried-Rtn
End-Evaluate
Example
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1) EVALUATE identifier
• May also use THRU clause to check range of values
Evaluate AgeWhen 0 Thru 19
Perform 400-Minor-RtnWhen 20 Thru 99
Perform 500-Adult-RtnEnd-Evaluate
Example
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2) EVALUATE TRUE
EVALUATE TRUEWHEN condition PERFORM …
…
Evaluate TrueWhen Age >= 0 And <= 19
Perform 400-Minor-RtnWhen Age >= 20 And <= 99
Perform 500-Adult-RtnEnd-Evaluate
Example
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2) EVALUATE TRUE
• Can also use with condition-names
Assume these condition names defined for Age field
05 Age Pic 99.88 Minor Values 0 Thru 19.88 Adult Values 20 Thru 99.
Example
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2) EVALUATE TRUE
Evaluate TrueWhen Minor
Perform 400-Minor-RtnWhen Adult
Perform 500-Adult-RtnEnd-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 conditionWHEN TRUE PERFORM …WHEN FALSE PERFORM …
Evaluate Age <= 19When True Perform 400-Minor-RtnWhen False Perform 500-Adult-Rtn
End-Evaluate
Example
11-39
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
11-40
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
11-41
Actions If Input Errors Occur
6. 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
11-42
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
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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
11-44
COBOL 2002+ Changes
• Restrictions on INSPECT statement limiting AFTER/BEFORE items to one-character literals or fields in REPLACING clause will be eleiminated
• VALIDATE statement introduced to check format of data field
11-45
Program Interrupts
• Termination of program caused by logic error
• List of common program interrupts and their causes follows
11-46
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
11-47
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
11-48
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
11-49
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
11-50
Chapter Summary
• Two types of program errors– Syntax errors– Logic errors
• Error control procedures can minimize errors but not eliminate them entirely
11-51
Chapter Summary
• Types of error control procedures– Range tests– Limit tests– Format tests– Tests for missing data– Sequence checks
11-52
Chapter Summary
• Other methods to validate data– INSPECT statement– Condition-names– EVALUATE verb– Verifying input data
11-53
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.