www.discogs.com
They have implemented a database with a pretty good representation of all the music releases (realizations, in other words), as submitted by volunteers (much like Wikipedia). How many of the questions posed here have already been resolved in a reasonable way by Discogs?
Then there was the late great Catraxx database, using much of the same relational structure as Discogs, but based on the MS Access engine. It can be used to write tags to audio files.