>Consider iTunes. iTunes stores the actual mp3 files on disk, but all metadata in a private database. Having two sources of truth causes endless problems. If yo

>Consider iTunes. iTunes stores the actual mp3 files on disk, but all metadata in a private database. Having two sources of truth causes endless problems. If you add a new song on disk you must manually tell iTunes to rescan it. If you want to make a program that works with the song database you have to reverse engineer iTunes DB format, and pray that Apple doesn't change it. All of these problems go away with a single system wide database. Well. Then you get Spotlight (on OSX, at least) - system-wide file/metadata/content search. It's great! It's also quite slow at times. Slow (and costly) to index, slow to query (initial / common / by-name searches are fast, but content searches can take a second or two to find anything - this would be unacceptable in many applications), etc. I like databases, but building a single well-performing one for all usages is quite literally impossible. Forcing everyone into a single system doesn't tend to add up to a positive thing.