Q: What's the difference between specifying a sequence of piano notes to be played (on musical staffs in standard musical notation, say) and specifying a computer program that will produce that same sequence of notes?
A: If a piece of music was no more than a linear string of notes, there would really be no point. The main idea is that the twelve musical pieces in this collection all have structure: they will contain loops, parts that repeat with variations, including loops within loops. At the lowest level, there may be a repeating figure like an arpeggio in the left hand. At the highest level, part of a piece may be played three times with variations each time (and perhaps a special coda at the end). A part might cycle through chord changes from i to vi to ii to v and then back again to i. Similar figures might be played high up on the piano and then lower on the piano and then back high up again. The piece might get louder gradually and then quieter again. Remember trig from high school? I use sine and cosine to talk about about going up and down on a curve that looks like an S on its side. Using structure in this way should result in specifications for musical pieces that are much more direct and concentrated than enumerating each individual note on musical staffs or in MIDI files.
That's the idea, anyway.