Set Field to the name of the field whose value the generator sets. When the event specified by the ApplyEvent property occurs, or when an application calls the Apply method, the TIBGeneratorField object calls the server to generate a field value and assigns that value to the specified field. 

Field must be the FieldName property of one of the fields in the associated dataset's Fields property list. The TIBGeneratorField object is associated with a dataset when it is the value of that dataset's GeneratorField property.