Specific media types for rdf vocabularies

I am involved in a standards effort to develop an rdf vocabulary for
describing software packages.[1]  We anticipate that a primary use for
the vocabulary will be to encode data regarding particular packages in
rdf/xml and to pass these rdf/xml files between agents (via http,
email, etc).  In that situation, is it appropriate to register a media
type specifically for this rdf-based vocabulary?  Or would using
generic rdf+xml media type be more appropriate?

Thanks in advance for your thoughts.

[1]: http://spdx.org

Peter
barelyenough.org