thanks everyone, this is great information to get me started!

to answer someone's question, I am confining myself to songs for this class. but some (carols?) may have dance origins that affected the allowable rhythms.

regarding the input of trained expert musicians vs impressions of untrained practitioners, I'm happy to listen to both and sort it out. I'm just asking for leads.

(which prompts the idea: to the extent that notation is adequate it should be possible to analyze tune relatedness computationally -- might be a good student project! but surely it has been done before).