I still maintain that all it would take to add tags to the unix filesystem is to start calling "files" "tags"
then use ln to add tags.
then use ln to add tags.
$ ls -l # How grep for files with tag "foo"?
$ find . -tag foo find . -samefile group/beatles/love_me_do
album/please please me/side 2/1
vocals/paul mcartney/love me do
vocals/john lennon/love me do
year/1963/love me do
group/beatles/love me do