Ensures that entered data is reasonable, complete, sensible and within the acceptable behaviour.
Range check: sets an upper and a lower boundary for the data; must lie between these two values
Type check: makes sure that the data entered is of the correct type (numeric, string, Boolean data/time)
Picture check: data entered requires a combination of numbers and letter. Cannot be applied to type check
Length check: ensures that the data cannot be more than a set number of characters
Presence check: data must be entered into a field. Computer insist that a value is entered for that field
Lookup check: takes the value entered and compares it against a list of values in a separate table