Extended features are defined and maintained by Data Exchange. These features are an extension of the existing features defined in the classifier. They are generated when you load or update a schema in DDW.

Data Exchange supports the extended feature $RSN for Enterprise Database Server. The RSN value can be used as a primary key. Data Exchange can uniquely identify a target record using the RSN value. If the RSN data item is not explicitly defined in the DASDL (a data item defined as type RSN) for the Extended data set, then Data Exchange will display the implicitly available RSN data item for the Extended data set as $RSN.