From MusicBrainz Wiki
- One track can appear on multiple albums/releases.
- New abstract entity - Work - http://lists.musicbrainz.org/pipermail/musicbrainz-users/2007-February/thread.html#15629
- AR types to build a tree of track versions - http://depmod.com/songs/personal_jesus.htm
- Multiple artists per track - http://musicbrainz.org/release/7ef09c54-f350-470e-a816-fbab654e37fc.html
- Track aliases in track listings ("track name variation") - http://musicbrainz.org/show/track/relationships.html?trackid=178484
- Artist aliases in track listings? ("artist name variation") - http://musicbrainz.org/release/f053d25d-38b7-4029-862f-0bbac7556262.html
- Multiple types on album level.
- Status on release level.
- Nested tracks listings to handle multi-disc releases - http://lists.musicbrainz.org/pipermail/musicbrainz-users/2007-May/015927.html
- Multiple artists per album - splits (e.g. http://musicbrainz.org/release/e8cf1c8d-4dad-4cb5-9213-e8460780015c.html)
- Multiple labels/cat#s per release - http://musicbrainz.org/release/67d1d053-a258-4e56-bf93-d1eafb96c673.html
- A special album type to identify classical albums.
- Different display for classical and non-classical albums (http://www.iclassics.com/productDetail?contentId=432, http://www.cduniverse.com/productinfo.asp?pid=3440451)
- "Artist" is meaningless here, ARs are the most important info (composer/orchestra/conductor/solists)
- Need a way to select primary performers for tagging, e.g. people who prefer performers as "artists" would probably expect to find http://musicbrainz.org/release/1e89147e-a776-48c2-a8a8-3ea3adc727ef.html under "Yo-Yo Ma", not "Yo-Yo Ma, Gilda Buttà & Roma Sinfonietta".
- 3-entity ARs to group orchestras and conductors together?