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Data Validation

Chapter 11. Data Validation. 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. Debugging Tips.

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Data Validation

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  1. Chapter 11 Data Validation

  2. 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

  3. Debugging Tips • For every IF statement, use 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

  4. Debugging Tips • Use 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 • Compile often

  5. 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

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

  7. Test Fields for Correct Format • Use NUMERIC class test to ensure field used in arithmetic operation has numeric value If Amt-In Is Not Numeric Perform 500-Err-Rtn Else Add Amt-In To WS-Total End-If Example

  8. Test Fields for Correct Format • Use ALPHABETIC class test if field must be alphabetic • COBOL has built in functions for the following: • 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 • IF X IS POSITIVE THEN …

  9. Checking for missing data • Check key fields if they must contain data If Soc-Sec-No = Spaces Perform 900-Err-Rtn End-If Example

  10. 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

  11. INSPECT … TALLYING • To count number of times a given character occurs INSPECT identifier-1 TALLYING ALL identifier-3 identifier-2 FORLEADING literal-1 CHARACTERS Format

  12. 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

  13. 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

  14. 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 FieldsResults X1 = bb82b Ct1 = 3 X2 = AB32C Ct2 = 5 X3 = 00060 Ct3 = 3

  15. 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

  16. 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 ItemsResults X4 = 05090 Ct4 = 2 X5 = 06762 Ct5 = 3

  17. 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

  18. 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

  19. INSPECT … REPLACING Examples Inspect Date-In Replacing All '-' By '/' Inspect SSNo Replacing All Spaces By '-' FieldBeforeAfter Date-In 10-17-02 10/17/02 SSNo 123 45 6789 123-45-6789

  20. INSPECT … REPLACING Examples Inspect X1 Replacing Leading 'A' By 'Z' Inspect X2 Replacing First 'R' By 'Q' FieldBeforeAfter X1 AAABBA ZZZBBA X2 RRSST QRSST

  21. 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

  22. Checking Coded Fields • Code often stored in field to shorten record and minimize typing using the 88 numbered field • For example, 'H' or 'S' may represent pay type of 'Hourly' or 'Salaried' • Use condition names to check validity of coded fields

  23. Checking Coded Fields Example 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 Data Division entries Procedure Division statements

  24. 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

  25. 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 • Can we use the inspect to solve our data entry problem of the lack of leading zeros and decimal spaces?

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

  27. 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

  28. 1) EVALUATE identifier • May also use THRU clause to check range of values Evaluate Age When 0 Thru 19 Perform 400-Minor-Rtn When 20 Thru 99 Perform 500-Adult-Rtn End-Evaluate Example

  29. 2) EVALUATE TRUE EVALUATE TRUE WHEN condition PERFORM … … Evaluate True When Age >= 0 And <= 19 Perform 400-Minor-Rtn When Age >= 20 And <= 99 Perform 500-Adult-Rtn End-Evaluate Example

  30. 2) EVALUATE TRUE Example • 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.

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

  32. 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

  33. 3) EVALUATE condition Example EVALUATE condition WHEN TRUE PERFORM … WHEN FALSE PERFORM … Evaluate Age <= 19 When True Perform 400-Minor-Rtn When False Perform 500-Adult-Rtn End-Evaluate

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

  35. Actions If Input Errors Occur 5. Use switch/If or 88 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

  36. Actions If Input Errors Occur • 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

  37. 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

  38. 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

  39. COBOL 2008 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 • Checks the format of data that is inputted from the user • Could also solve are input problem

  40. Common Program Interrupts • Data Exception • Performing operations on field containing blanks or other nonnumeric characters • Arithmetic operation • Comparison • Failing to initialize subscript or index

  41. 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

  42. 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

  43. 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

  44. Chapter Summary • Two types of program errors • Syntax errors • Logic errors • Error control procedures can minimize errors but not eliminate them entirely • Page 456 – way to input data file name from users instead of always hard-coding it. • READ…INTO Statement page 456 • INITIALIZE statement

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

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

  47. 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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