System Development Lifecycle

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System Development Lifecycle

• Verification and Validation

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Learning Objectives

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

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Design Phase

• Continued

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Data Validation Routines

• Check input data is sensible before accepting and
  then processing it.

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Presence Check

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

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Range Check

• This checks that the data lies within a specified
  range of values.
• e.g.
• The month of a person's DOB should lie between 1
  and 12.
• A telephone bill amount is less than some maximum
  value for consumer bills.

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Type / Format Check

• A check that data is of the right type.  
• E.g.
• Number, Text etc
• For currency data - digits point digit digit

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Character check

• Check for / Reject particular characters.
• E.g.
• No numbers in text.
• Hyphen or apostrophe

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Length Check

• Checks that fields have the correct number of
  characters / digits.
• E.g.
• A bank account number may always be 10 digits
  long.
• A date must have at least 6 numbers in it.
• A phone number has 12 numbers.

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Check digits

• Used for numerical data.
• An extra digit is added to a number which is
  calculated from the number using modular division
  (dividing by a number and using the remainder as
  the extra digit) .
• The computer divides by the same number to check
  this digit.
• E.g. The ISBN number on a book is 4534301
• 453430 / 9 ... remainder 1, so 1 is the check
  digit.

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Batch Totals

• This checks for missing records.
• Numerical fields may be added together for all
  records in a batch.
• The batch total is entered and the computer
  checks that the total is correct.
• E.g. Add the 'Total Cost' field of a number of
  transactions together.

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Hash Totals

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

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Verification

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

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Double entry

• Typing the data in twice and comparing the two
  copies.
• Time consuming
• Costly

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Proofreading data

• Checking what is on the screen is the same as on
  the input document.
• Time consuming
• Costly

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Plenary

• What is validation?
• Check input data is sensible before accepting and
  then processing it.
• What is verification?
• Used to prevent errors occurring when data is
  copied from one medium to another.

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Plenary

• List all validation methods.
• List both verification methods.