When the developer Erik Kemp designed the first metadata system for MP3s in 1996, he provided only three options for attaching text to the music. Every audio file could be labeled with only an artist, song name, and album title.
Kemp’s system has since been augmented and improved upon, but never replaced. Which makes sense: Like the web itself, his schema was shipped, good enough, and an improvement on the vacuum which preceded it. Those three big tags, as they’re called, work well with pop and rock written between 1960 and 1995. This didn’t prevent rampant mislabeling in the early days of the web, though, as anyone who remembers Napster can tell you. His system stumbles even more, though, when it needs to capture hip hop’s tradition of guest MCs or jazz’s vibrant culture of studio musicianship.
And they really, really fall apart when they need to classify classical music.