Something that might be relevant for analyzing tune relationships. Look at the display here:

http://abcnotation.com/tunePage?a=dl.dropboxusercontent.com/u/420691/tune-a-day/0433

The graph at the right shows relationships with other tunes known to the ABC corpus. I haven't really used it but it might be worth trying to understand what it does. (Probably not enough - maybe Pamela can improve it?)