file/directory only library option

[the_bertrum]

The big problem with the tag idea is that when people are given a text field where they can enter anything, they will.  You can't have meaningful indices and queries without key integrity.  Music tags are the same way unless you get all your files from the same commercial source.  You don't want to see what my library looks like. 

What you say for tags is also true of your folder hierarchy, the folder names are after all just free text and it is only because you take care to put things in the right place that the system remains in order. Take the same care over your tags, and all is well.