Define a presence check.
Ensures that data has been entered into a field.
Define a length check.
Ensures that data entered has the correct number of characters or doesn’t exceed a certain number of characters.
Define a type check.
Ensures that data entered is of the correct type.
Define a format check.
Ensures data entered is of an exact format, possibly matching an input mask.
Define a range check.
Ensures that entered data is within an acceptable range.