the primary theme exposed in this piece needs no introduction, but starts right off the bat. this section is a parallel period, with a half cadence in the 8th measure and a PAC in the 16th. the developmental section comes next. the theme played here is very similar to the expository section, but certain chords and harmonies differ--it sounds much more bittersweet and poignant here. the recognizable melody leads to a new one when the key changes. i think this section is transitional because it eventually connects this passage to the melody once heard at the beginning. this section is also fairly unpredictable and there are abrupt dynamic contrasts; it is rather hard to follow. the main melody only sticks around 8 measures or so until the key changes again. the next 12 measures (followed by a sweet cadence back in Ab major) also act as a transitional function into a new expository function at the trio. i'm uncertain if i should call it an expostiory function...but the trio sounds like it to me. After this first melody is heard for 16 measures (a parallel period once again), there is a developmental section that sounds very similar, but has some different harmonic activity.
There is a D.C. to the alegretto section (the beginning) after the trio, so the original theme is heard again and all is well again. Although the melody was passed around a lot, the main passage and key of Ab major come back again to please the listener.