A Level IT

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A Level IT

• Verification and Validation

IT02 Chapter 16 p85
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Data capture

• DATA CAPTURE
• Method used depends on
• Speed
• Accuracy
• Cost
• Direct data entry systems have most of these
  benefits
• TASK - Name 2 DDE methods
• Hint - Codes and Optical methods

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Data Collection Form
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Data Entry Process

• What are the processes involved in entering the
  data?
• Fill in the form
• Collect form deliver to data entry clerk
• Store form
• Enter data
• Store form
• What errors could occur!

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Types of Error

• Customer mistake
• Form filled in incorrectly
• Transcription error
• Operator error in copying data from the form
• Lost Form
• Double entry
• Incorrect data transmission

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Batch processing

• In a batch processing system, documents such as
  sales orders are collected into batches of
  typically 50 documents.

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Batch processing

• A data control clerk is responsible for
• Counting the documents
• Checking each one visually to see that the
  customer has entered essential details
• Calculating a control total of some crucial field
  such as Total Payable, for the entire batch
• Calculating hash totals of other fields such as
  size or quantity (see later)

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Batch processing

• Filling in a batch header document to show, e.g.
• batch number
• number of documents in batch
• date received
• control total
• hash total
• logging the batch in a log book

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Definitions

• Verification
• A verification check ensures that data is
  correctly transferred into a computer from the
  medium that it was originally stored on.
• Validation
• A validation check is an automatic check made by
  a computer to ensure that any data entered into
  the computer is sensible.

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Validation checks

• Almost every field in a database can have some
  type of validation to ensure that data entry is
  accurate.

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Validation checks

• Presence check
• Certain fields such as customer number, item
  code, quantity etc must be present.
• Format check (also called picture check)
• e.g. code may have a pattern of 2 letters
  followed by 4 numbers. The quantity and price
  must be numeric.
• Range check
• A card expiry date must have a month number
  between 1 and 12, and date must be after today

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Validation checks

• Specific options
• e.g. Sex (M / F)
• File lookup check
• If the customer has filled in their customer
  number, the computer can look this up on the
  customer file and display the name and address.
  The data entry operator can check that it
  tallies.
• Check digit check. (described later)
• Batch header checks
• Total number of records in the batch should be
  calculated and compared with batch header.

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Check digits

• Code numbers such as a customer no., employee no.
  or product no. are often lengthy and prone to
  error.
• One way of preventing these errors is to add an
  extra digit to the end of a code number which has
  been calculated from the digits of the code
  number.
• In this way the code number with its extra check
  digit is self-checking.
• Best-known method of calculating check digits is
  the modulus-11 system, which traps over 99 of
  all errors.

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Method

• 1.   Each digit of the code number is assigned a
  weight.
• The right hand (least significant) digit is given
  a weight of 2, the next digit to the left 3 and
  so on.
• 2.   Each digit is multiplied by its weight and
  the products added together.
• 3.   The sum of the products is divided by 11 and
  the remainder obtained.
• 4.   The remainder is subtracted from 11 to give
  the check digit. The two exceptions are
• If remainder is 0, check digit is 0, not 11
• If remainder is 1, check digit is X, not 10

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Example

• To calculate the check digit for the number 1587
• Original code number 1 5 8 7
• Weights 5 4 3 2
• Multiply digit by its weight 5 20 24 14
• Add products together 5 20 24 14 63
• Divide by 11 5 remainder 8
• Sub remainder from 11 11 - 8 3
• Check digit 3.
• Complete code number is 15873.

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Checking

• To check that a code number is valid, it is not
  necessary to recalculate the check digit
  completely. If the check digit itself is assigned
  a weight of 1, and the products of the digits
  (including the check digit) and their respective
  weights are calculated, their sum will be
  divisible by 11 if the check digit is correct.

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Verification

• Entering data twice and comparing the two
• Common in batch processing for a second data
  entry operator to key in a batch of data to
  verify it
• Example
• When setting a password, you are usually asked to
  key the password in a second time.
• This is to ensure that you didnt make a keying
  error the first time, as it is not echoed on the
  screen.

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Detecting Transmission Errors

• Errors can occur when moving data
• Parity bits
• Even parity
• 01010001 odd 1 added at end 010100011
• 01010011 even 0 at end 010100110
• Checks take place a beginning and end of
  transmission.

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Accuracy v Validity

• Data can be valid but inaccurate
• Example
• A car might be described as a Vauxhall Corsa on a
  form
• Validation checks can say that this is a valid
  car type
• But if form filled in incorrectly database will
  be wrong
• Only the data owner can confirm correctness.

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Accuracy v Validity

• Consider following sets of data. What validity
  checks could take place and could data be valid
  but inaccurate.
• School Student database
• Contains Name, Sex, DoB, Address, Subjects
• Form on page 85

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Tasks

• Read the Case Study on page 89.
• Answer the questions a-e
• Answer Q 2, 3, and 5 for homework.