Purpose and types of Validation

Purpose and types of Validation

1. Key Words

   • Transcription error - error made when typing data in using a document as the source of the data
   • Transposition error - error made when characters are swapped around so they are in the wrong order
   • Range check - data validation technique which checks that the data input to a computer is within a certain range
   • Validation checks - checks a developer of a solution creates, using the software, in order to restrict the data that a user can enter, so as to reduce errors

2. The validity and correctness of data

   • for a piece of data to be valid, it has to obey certain rules
     • for example, if a field has been set for the entry of a number, and a letter is entered instead, then the letter is not a valid piece of data for that field
       • this shows that there is a difference between the correctness and validity of data
   • if the surname 'James' was entered incorrectly as 'Jones' then it would be accepted into the database, as 'Jones is as much a piece of data are valid yet one is incorrect.

3. types of error which can occur during data entry

   • transcription errors
     • transcription involves the transferring of data to the computer, usually by keying it in.
     • transcription can also involve typing what a person says into the computer
     • problems when keying in data
       • problems with understanding speech
       • a caller not spelling out unusual words or names
       • poor handwriting
       • misiterpretation
       • typing mistake
   • transposition errors
     • transposition errors are easy to make when typing at high speed and involve the accidental swapping of characters
     • errors can be spotted during the proof reading process and it is also possible to spot some of them using spellcheckers
     • important numbers such as account numbers, employee numbers, VAT numbers, etc., make use of check digits which enable checking on the accuracy of the input of these numbers

4. validation

   • ... is a check performed by a computer program during data entry, validation is the process which ensures that data accepted for processing is sensible and reasonable
   • validation is performed by the computer program being used and consists of a series of checks called validation checks

5. validation checks

   • ... used to restrict the user as to the data they can enter
   • Data type checks - these check if the data being entered is the same type as the data being entered is the same type as the data type specified for the field.
   • presence checks - some database fields have to be filled in, whilst others can be left empty
   • length checks - checks to make sure that the data being entered has the correct number of characters in it
   • file/table lookup - are used to make sure that codes being used are the same as those used in a table or file of codes
   • cross field checks - the data in more than one field often need to be checked together to make sure they make sense
   • range check - are performed on numbers, they check that a number being entered is within a certain range
   • format check - are performed on codes to make sure that they conform to the correct combinations of characters

6. Remember

   • not only is there a requirement that data is error free, it is essential that data is up-to-date
   • data that is not kept up-to-date will be accurate at the time it was entered but changes to details such as name. address, etc., will mean that errors start to creep in
   • if personal data is stored, then there is a requirement under the Data Protection Act 1998 to keep such details up-to-date

7. check digits

   • ... are added to important numbers such as account numbers, International Book Numbers (ISBNs), Article numbers, etc.
   • these numbers are placed at the end of the block of numbers and are used to check that the numbers have been entered correctly into the computer
   • when the number is entered, the computer performs a calculation using all the numbers to work out this extra number. If the calculation reveals that the extra number (called the check digit) is the same as that calculated by the other numbers, it means that all the numbers have been entered correctly

8. limitations of error checking

   • reduce the amount of typed input to a minimum
   • allow a user to type in their details
   • allow a user to check and confirm their details are correct
   • use verification and validation methods