Validation

Ensures data being entered is both sensible and possible

Good validation can prevent program from breaking (or even hacking)

Range Check (data must be numerical data in a range)

Presence Check (Data must be entered)

Type Check (Data must be a certain acceptable data type)

Lookup check (Data must be within a list of options)

Length Check (Usually for string, the length of the string must be within a given range)

Format Check (The data has to conform to a specific format)

Usually validation is done automatically by computer

Most of the time, more than one type of validation check might be needed for a set of data

To verify if a series of number is entered / transferred correctly

Usually check digit is the last digit

A special algorithm is used to calculated the check digit