Rating is a new feature which has been introduced with the server release of November 23th, 2008.
It allows users to rate MusicBrainz entities (artists, labels, releases and tracks).
Each user rating is a number between 1 and 5. Then the system aggregate users ratings to compute the average community rating.
By default community rating is shown. As soon as user rates an entity, he/she will only see his/her own rating.
Display of ratings can be disabled in User Preferences for those who prefer not to use or see ratings.
Meaning of the Colors
The XMLWebService has been updated in order to allow to retrieve or update rating via WS in a similar way to how FolksonomyTagging works.
Either by the new /rating resource for submitting/retriving one specific rating:
wget --user=<editor name> --password=<password> --post-data=id=8f6bd1e4-fbe1-4f50-aa9b-94c450ec0f11\&entity=artist\&rating=3 http://test.musicbrainz.org/ws/1/rating
or by using the new inc parameters
ratings, user-ratings with the artist, label, release or tracks resources as described in XMLWebService.