Er, surely “genre” is also not inherently an album-level property? In fact the ID3v2 TCON ‘genre’ tag is explicitly associated with a track. So it’s perfectly possible to have an album with a mixture of genres.
Every file tag is explicitly associated with a track, including obviously non-track-level things like “Album Artist”–this is a technical compromise inherent to file-based tagging, and not–by itself–a good argument for making all data track-based.
Prior to the advent of file-based tagging, there is ample historical precedent for genre as an album-level classification.
- It’s how records were sold in record stores.
- It’s how every major music metadata database (including the “big 3”: Rovi, MusicBrainz, and Discogs) treats the data
- It’s how record labels describe their content when publishing their catalogs to retailers.
What we take away from this is: track-level genre distinctions within an album are an artifact of people managing files using file-level tags, and not something inherent to the way music is published or cataloged.
So, like the other metadata databases out there, we’ve put genre at the album level. When importing data from file tags, we aggregate track-level genre tags and pull them up to the album level.