For example, a secondary school student is likely to be aged between 11 and 16. The computer can be programmed only to accept numbers between 11 and 16. This is a range check.
However, this does not guarantee that the number typed in is correct. For example, a student's age might be 14, but if 11 is entered it will be valid but incorrect.
There are a number of validation types that can be used to check the data that is being entered.
|Validation type||How it works||Example usage|
|Check digit||The last one or two digits in a code are used to check the other digits are correct||Bar code readers in supermarkets use check digits|
|Format check||Checks the data is in the right format||A National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number|
|Length check||Checks the data isn't too short or too long||A password which needs to be six letters long|
|Lookup table||Looks up acceptable values in a table||There are only seven possible days of the week|
|Presence check||Checks that data has been entered into a field||In most databases a key field cannot be left blank|
|Range check||Checks that a value falls within the specified range||Number of hours worked must be less than 50 and more than 0|
|Spell check||Looks up words in a dictionary||When word processing|