Validation
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.
Types of validation
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. The currency of the UK is GBP or Pound Sterling (eg £23.45) but in the USA the currency is USD or US Dollar (eg $5.20). A date can be formatted in different formats, eg 28/01/1999; 28/1/99; 28 January 1999. |
| 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 |
| Validation type | Check digit |
|---|---|
| How it works | The last one or two digits in a code are used to check the other digits are correct |
| Example usage | Bar code readers in supermarkets use check digits |
| Validation type | Format check |
|---|---|
| How it works | Checks the data is in the right format |
| Example usage | A National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number. The currency of the UK is GBP or Pound Sterling (eg £23.45) but in the USA the currency is USD or US Dollar (eg $5.20). A date can be formatted in different formats, eg 28/01/1999; 28/1/99; 28 January 1999. |
| Validation type | Length check |
|---|---|
| How it works | Checks the data isn't too short or too long |
| Example usage | A password which needs to be six letters long |
| Validation type | Lookup table |
|---|---|
| How it works | Looks up acceptable values in a table |
| Example usage | There are only seven possible days of the week |
| Validation type | Presence check |
|---|---|
| How it works | Checks that data has been entered into a field |
| Example usage | In most databases a key field cannot be left blank |
| Validation type | Range check |
|---|---|
| How it works | Checks that a value falls within the specified range |
| Example usage | Number of hours worked must be less than 50 and more than 0 |