Each Artist in MusicBrainz has a unique ArtistID, which is an absolute URI. It has the form
UUID is a Universally Unique Identifier in its 36 character ASCII representation. In situations where the context is clear (such as file tags), just the
UUID part can be used, leaving a relative URI.
http://musicbrainz.org/artist/72c536dc-7137-4477-a521-567eeb840fa8 is a unique identifier for the artist Bob Dylan.
72c536dc-7137-4477-a521-567eeb840fa8 is a relative URI for this artist.