Does the Audience element require a controlled vocabulary?
No NSDL_DC elements require a controlled vocabulary, but controlled vocabularies are a good idea. Collection builders are encouraged to use the NSDL_DC Audience vocabulary and then repeat the Audience element to use their own local vocabulary. If possible, please indicate you are using the NSDL_DC vocabulary by including the XML attribute: xsi:type=” nsdl_dc:NSDLAudience”. This allows for easier vocabulary interpretation.