Release groups usage guideline
Current Musicbrainz server release feature a concept called Release Groups. Just as the name suggests, it groups several releases together in one entity. Since this is not obviously clear, this page aims to explain the difference and to give some guidelines on how to handle them.
Both release groups and releases are "albums" in colloquial sense, but with a slight difference: a release is something you can buy as media, e.g. a CD box, a vinyl record etc, while a release group embraces the concept of an album -- it doesn't matter how many CDs it had or whether it has been released as a cassette. When an artist tells you "We've released our new album", he's talking about a release group. When his publisher says "This new album gets released next week in Japan and next month in Europe", he's talking about several releases belonging to the release group the artist has told you about.
Musicbrainz automatically considers a single release to be part of a release group, even if this group only contains this one release. Therefore, grouping releases only requires merging several release groups. The following criteria should help you to decide which releases should be merged and which should not.
Release group examples that should be merged
- Slightly different versions of the same release, e.g. variations of Nirvana's "Nevermind"
- A release with a bonus disc, e.g. The Corrs' "In Blue"
- A multiple-disc compilation, e.g. a release group "Bravo Hits 64" containing both CDs from the jewel case
- A multiple-disc release in a box, e.g. Richard Wagner's "Ring der Nibelungen"
- Multiple-disc "Best of" compilations, e.g. Joe Dassins "Intégrale"
Release group examples that should not to be merged
- Compilation series like "Café del Mar" or "That's what I call music!". A particular double-CD is usually a release group, but not the whole series.