System Development System Development LifecycleLifecycle

Verification and ValidationVerification and Validation

Learning ObjectivesLearning Objectives

Describe the need for the accurate input of data and the ways in which we can check that the data is correct.

Identification

Feasibility study

Information Collection

Analysis

DesignDevelopment and Testing

Implementation

Maintenance

Obsolescence

Design PhaseDesign Phase

ContinuedContinued

Data Validation RoutinesData Validation Routines

Check input data is Check input data is sensiblesensible before before accepting and then processing it.accepting and then processing it.

Presence CheckPresence Check

This checks that important data is actually This checks that important data is actually there and has not been missed out. there and has not been missed out. E.g. Customers may be required to give their E.g. Customers may be required to give their

telephone numbers or surname.telephone numbers or surname. Can only be used to check something has been Can only be used to check something has been

input not check if the input is sensible.input not check if the input is sensible.For example, if asked to validate a name, a presence For example, if asked to validate a name, a presence check cannot be used as “something” has already check cannot be used as “something” has already been entered. You can only use a presence check been entered. You can only use a presence check on a input to check if an input has been made.on a input to check if an input has been made.

Existency

A code exists. E.g.

Bar code exists in the stock file.

Dates actually exist e.g. 31/04/07 or 29/02/07 do not exist but are in the correct format.

Consistency checkConsistency check

Checks fields to ensure data in these Checks fields to ensure data in these fields corresponds.fields corresponds. e.g. If Title = "Mr.", then Gender = "M".e.g. If Title = "Mr.", then Gender = "M".

Range CheckRange Check

This checks that the data lies within a This checks that the data lies within a specified range of values. specified range of values. e.g. e.g.

The month of a person's DOB should lie between 1 The month of a person's DOB should lie between 1 and 12.and 12.

A telephone bill amount is less than some A telephone bill amount is less than some maximum value for consumer bills.maximum value for consumer bills.

TypeType

A check that data is of the right type.  A check that data is of the right type.   E.g. E.g.

Number, Text etc…Number, Text etc…

Format CheckFormat Check

A check that data is in a specified format.  A check that data is in a specified format.   E.g. E.g.

Dates have to be in the format DD/MM/YYYY. Dates have to be in the format DD/MM/YYYY.

Most ID numbers and codes have requirements Most ID numbers and codes have requirements which can undergo format checking.which can undergo format checking.

Only for regular expressions where there is a strict Only for regular expressions where there is a strict format requirement where the number of format requirement where the number of characters and/or digits for each part of the format characters and/or digits for each part of the format is also restricted.is also restricted.

Character checkCharacter check

Check for / Reject particular characters.Check for / Reject particular characters. E.g.E.g.

No numbers in text.No numbers in text.

Hyphen, apostrophe or @ followed by a . (email Hyphen, apostrophe or @ followed by a . (email addresses).addresses).

Length CheckLength Check

Checks that fields have the correct Checks that fields have the correct number of characters / digits.number of characters / digits. E.g. E.g.

A bank account number may always be 10 digits A bank account number may always be 10 digits long.long.

A date must have at least 6 numbers in it.A date must have at least 6 numbers in it.

A phone number has 12 numbers.A phone number has 12 numbers.

Check digitsCheck digitsUsed for numerical data. Used for numerical data.

An extra digit is added to a number which is calculated An extra digit is added to a number which is calculated from the number using modular division (dividing by a from the number using modular division (dividing by a number and using the remainder as the extra digit) .number and using the remainder as the extra digit) .

The computer divides by the same number to check this The computer divides by the same number to check this digit. digit.

e.g. modulo-11 multiplies each digit by its digit position, adds the e.g. modulo-11 multiplies each digit by its digit position, adds the totals together and divides the result by eleven.totals together and divides the result by eleven.

An ISBN number on a book is 420351An ISBN number on a book is 420351__ where where __ is the check digit. is the check digit. The check digit is digit position 1 The check digit is digit position 1 (as it is the 1st place value(as it is the 1st place value).). Sum = (1*2)+(5*3)+(3*4)+(0*5)+(2*6)+(4*7)Sum = (1*2)+(5*3)+(3*4)+(0*5)+(2*6)+(4*7) = 2+15+12+0+12+28 = 69= 2+15+12+0+12+28 = 69 11*6 = 6611*6 = 66 So 69/11 = 6 remainder So 69/11 = 6 remainder 69-6669-66 = = 3 3 which is the check digit.which is the check digit.

So the full number entered is So the full number entered is 42035142035133

Batch TotalsBatch Totals

This checks for missing records. This checks for missing records.

Numerical fields may be added together Numerical fields may be added together for all records in a batch. for all records in a batch.

The batch total is entered and the The batch total is entered and the computer checks that the total is correct. computer checks that the total is correct. E.g. Add the 'Total Cost' field of a number of E.g. Add the 'Total Cost' field of a number of

transactions together.transactions together.

Hash TotalsHash Totals

This is just a batch total done on a This is just a batch total done on a meaningless field. meaningless field. E.g. Add the Telephone Numbers together for E.g. Add the Telephone Numbers together for

a number of Customers.a number of Customers.

Other Validation ChecksOther Validation Checks

http://en.wikipedia.org/wiki/Data_validation

Verification

Used to prevent errors occurring when Used to prevent errors occurring when data is copied from one medium to data is copied from one medium to another. another. e.g. paper to disk, disk to disk, memory to e.g. paper to disk, disk to disk, memory to

diskdisk

Double entryDouble entry

Typing the data in twice and comparing Typing the data in twice and comparing the two copies.the two copies. Time consumingTime consuming CostlyCostly

Proofreading dataProofreading data

Checking what is on the screen is the Checking what is on the screen is the same as on the input document. same as on the input document. Time consumingTime consuming CostlyCostly

PlenaryPlenary

What is What is validationvalidation?? Check input data is Check input data is sensiblesensible before accepting before accepting

and then processing it.and then processing it.

What is What is verificationverification?? Used to prevent errors occurring when data is Used to prevent errors occurring when data is

copied from one medium to another. copied from one medium to another.

PlenaryPlenary

List all validation methods.List all validation methods.

List both verification methods.List both verification methods.