Also, Pamela, there is an analytical system called Shenkerian Analysis that allows for the sort of comparisons that you're talking about. Here is the Wikipedia Article which explains it--at least sort of. Granted, it is a bit controversial(Among music theorists, it is a "Drink the Kool Aid" sort of thing) but he basically looked at the underlying direction and structure of a melody and the the smaller journeys that it made from each step, I find it very helpful both in writing and performing. It could be said that he took the obvious and made it arcane, though.