Fresno has identified my question here.
And that page does explain much, though i was hoping for a less human/text definition.
Musicbrainz is no doubt a very deep and complex database with a complex api, and a structured definition would really help in using it
I'm not trying to be being critical here and would bet not having it is at least partially a manpower shortage, but my opinion would be such a hard typed definition would be considerably more useful than a soft typed diagram/discussion type page as is.
I know the next post will be telling me to get busy and create it
thanks for the help