Instead of a direct reference, using the domain Reference attribute enables the declaration of a domain class that corresponds to a common parent class. For instance, if a Web service provides geographic coordinates (e.g. latitude, longitude) and an input operation of a UI component can process these geographic coordinates to display in a map, both interfaces can be added to a category based on the same data type. A domain class provides a solid cooperation with a classification and facilitates the discovery of suitable UI components for Web service operations.