Somewhat unfortunately, the namespace URIs for the Unity subjects are http://bitbucket.org/nxg/unity/ns/unit#, http://bitbucket.org/nxg/unity/ns/syntax# and http://bitbucket.org/nxg/unity/ns/schema# (the library was at one time hosted at bitbucket, but the repository has been migrated away). Although these are of course somewhat arbitrary, it is undesirable that they are still at bitbucket. It would be good to change these, but that probably can't happen before some future version of the software.