Validating text files
This is the same as setting the Required field property to Yes.
For example, a date field might have a validation rule that disallows values in the past. Record Validation Rule You can use a record validation rule to specify a condition that all valid records must satisfy.Validation text lets you provide a message to help users who input data that is not valid.When data is entered, Access checks to see whether the input breaks a validation rule – if so, the input is not accepted, and Access displays a message.You can use an expression to perform calculations, manipulate characters, or test data. For example, an expression can check for one of a series of values, such as "Tokyo" Or "Moscow" Or "Paris" Or "Helsinki".Expressions can also perform mathematical operations. For example, the expression You can add a field validation rule and/or a record validation rule.
A field validation rule checks input to a field, and is applied when the focus leaves the field.