Essential datum is the pitch of the note. We will use the MIDI definition of the pitch: an integer value between 0 and 127, based on C3 = pitch 60.
But we also need the position of the note to determine which kind of note error we have (wrong note, skip note or extra note. See "evaluation criteria" for more details). Position will be defined as a three values structure: [measure number, beat number, beat fraction].