to get back to my point about style,and why it relates to this thread,very often if a song can be sung successfully unaccompanied it can be classified as a folk song,but it is only one ingredient of many that makes a song a folk song.
youll never walk alone,wheelbarrw song, Athenry,are all sung unaccompanied and work as folk songs in certain contexts,[example at football matches]in fact the sensation of thousand people singing youll never walk alone,is unbelievable,but they dont work out of that context[athenry perhaps does, although I hate it]or if sung in a folk club,neverthelees they are folk songs.
so context or environment, and style are as important [imo]or possibly more important than process.
of course flamenco music is folk music too,but it has different roots.