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Checking Data

Chapter 7

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In this lesson we are going to discuss the followingpoints:

Reasons for errors.

Consequences of errors.

How are errors avoided?- Verification- Validations

Types of error- Transcription errors- Transposition errors

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Reasons for errors:

In many systems an input document may be used.

Either the data on this document keyed into the computer, reasons for

error are:Transcription (misreading)Typing mistakes.Incorrect data.

Or the document is input directly to the computer:

Transposition (devices read 5 instead of s and 0 instead of o).Bad hand writing. Incorrect data.

Computers can produce accurate results (e.g. payslips, bills,Invoices, etc) only if the data put into them is accurate.

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Consequences of errors:

Customers become angry if they are sent bills that are too largeand companies lose money if bills are too small.

Wrong decisions are made by the managers because thedecisions are based on wrong information

A company could be prosecuted under Data Protection Act1998 if the incorrect information causes the person concernedsome kind of loss. For instance if someone lost a job because acomputer contained wrong information about a criminal record.

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How errors avoided?

Verification.

Validation.

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Verification:

Verification is checking that what is on theinput document is exactly the same as whatis entered into the computer.

Notice that this dose not mean that it is

correct, since the details on the form couldbe incorrect.

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Methods of Verification

Double Entry.

Proof reading.

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Double Entry:

Double entry is when two people typing in the

same data and only if the data is identicalthen it is accepted for further processing.

The problem with double entry is that two

people need to be paid for doing the samejob.

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Validation:

Validation is the process of detecting any

data that is inaccurate, incomplete orunreasonable. It is performed by a computer

program

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Types of Validiation Check:

Character type check-

Range Check-

Presence Check

length checks

Spelling Checker

Lookup Table:

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Character type check-

Character checks make sure that the right

type of characters have been entered.

Such checks detect numbers where

characters should have been entered.

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Range Check

Range checks are performed on numbers to

make sure that they lie within a specifiedrange.

If all data should be over 60, so if the typist

entered 18 instead of 81 then the rangecheck detects this error.

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Presence Check-

When entering data into a database the completion ofsome fields may be optional.

There are certain field must contain data the systemwill not allow them to remain blank.

An example of this would be a National InsuranceNumber in a payroll system.

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Length checks

Sometimes a certain item of information is always of a

certain length.

A national insurance number always has nine

characters.

If it has more or fewer than nine characters then the

length check will alert you to the fact that it has been

entered incorrectly.

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Spelling Checker-

Any software where accurate text is needs to

be entered can have a spell checker facility

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Lookup table

Stock items are given a unique code to identify them.

Whenever this code is used, it is checked against a

table stored by the computer to make sure that it is a

valid stock code.

if the code is not in the table it is rejected, thus

prevending any processing using incorrect codes.

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Types of Errors:

Transcription errors.

Transposition errors.

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Transcription errors:

Transcription errors occur due to misreading

or mistyping data.

This may cause by bad hand writing or

confusing, for instance the number 5 with the

letter S or number 0 with the letter O.

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Transposition error

Transposition errors occur when two digits orletters are swapped around.

like you type ot instead of to or 5124 insteadof 52140.

It is estimated that 70% of all errors aretransposition errors.

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Home work:

Things to do page 61 ( 1,2 and 3)