Validation rules are criteria that a DataWindow object uses to validate data entered into a column by users. They are DataWindow Designer specific and therefore not enforced by the DBMS.
Validation rules assigned in the Database painter are used by default when you place columns in a DataWindow object. You can override the default rules in the DataWindow object painter.
A validation rule is an expression that evaluates to either TRUE or FALSE. If the expression evaluates to TRUE for an entry into a column, DataWindow Designer accepts the entry. If the expression evaluates to FALSE, the entry is not accepted and the ItemError event is triggered. By default, DataWindow Designer displays a message box to the user. You can customize the message displayed when a value is rejected.
You can also code the ItemError event to cause different processing to happen.
For more information, see the chapter on using DataWindow objects in the Programmer’s Guide.
