The ability to create a domain that populates a features attribute table field based on spatial location. Similar to a relationship class without the composite nature. The feature is not deleted and the domain is easily deployed accross multiply feature classes. An example: When working with a city street network dataset you have a polygon annexation feature dataset , polyline street feature and point mile marker feature. You digitize a new road and the field for the annexation area is automatically populated based on its intersection with annexation. Similarly the mile marker street attribute is automatically populated based on is intersection with street.