In computing, the process of checking input data to ensure that it is complete, accurate, and reasonable. Although it would be impossible to guarantee that only valid data are entered into a computer, a suitable combination of validation checks should ensure that most errors are detected. The term is also commonly used to describe the process of testing software applications for any bugs and defects before release.
Common validation checks include:
Each input data item is checked to ensure that it does not contain invalid characters.
For example, an input name might be checked to ensure that it contains only letters of the alphabet, or an input six-figure date might be checked to ensure it contains only numbers.
The number of characters in an input field is checked to ensure that the correct number of characters has been entered. For example, a six-figure date field might be checked to ensure that it does contain exactly six digits.
The arithmetic total of a specific field from a group of records is calculated - for example, the hours worked by a group of employees might be added together - and then input with the data to which it refers. The program recalculates the control total and compares it with the one entered to ensure that entry errors have not been made.
An otherwise meaningless control total is calculated - for example, by adding together account numbers. Even though the total has no arithmetic meaning, it can still be used to check the validity of the input account numbers.
Parity bits are added to binary number codes to ensure that each number in a set of data has the same parity (that each binary number has an even number of 1s, for example). The binary numbers can then be checked to ensure that their parity remains the same. This check is often applied to data after they have been transferred from one part of the computer to another; for example, from a disk drive into the immediate-access memory.
A digit is calculated from the digits of a code number and then added to that number as an extra digit. For example, in the ISBN (International Standard Book Number) 0 631 90057 8, the 8 is a check digit calculated from the book code number 063190057 and then added to it to make the full ISBN. When the full code number is input, the computer recalculates the check digit and compares it with the one entered. If the entered and calculated check digits do not match, the computer reports that an entry error of some kind has been made.
An input numerical data item is checked to ensure that its value falls in a sensible range. For example, an input two-digit day of the month might be checked to ensure that it is in the range 01 to 31.
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