Just came across this neat piece of work where a group has put together every category imaginable for classifying music. In their words: “The Music Ontology Specification provides main concepts and properties fo describing music (i.e. artists, albums, tracks, but also performances, arrangements, etc.) on the Semantic Web.”
Edit (March 2014) is now at: http://musicontology.com/
Could come in handy as more software is developed around music making and music performances.