Verification

1
Verification Validation
2
Batch processing

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

• A data control clerk is responsible for
• 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

4
Validation checks

• Almost every field in a database can have some
  type of validation to ensure that data entry is
  accurate.
• Presence checkCertain 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 checkA 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 optionse.g. Sex (M / F)
• File lookup checkIf 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.
• Look-up list checkThe operator chooses from a
  list of valid values.
• Check digit check. (described later)
• Batch header checksTotal number of records in
  the batch should be calculated and compared with
  batch header.

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Check digits

• Code numbers are often lengthy and prone to
  error.
• E.g. customer no., employee no. or product no.
• 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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Modulus-11 Check Digit

• 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.
• Each digit is multiplied by its weight and the
  products added together.
• The sum of the products is divided by 11 and the
  remainder obtained.
• 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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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.