Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/4
M:6/4
K:D
['B A G F- F/E/ D f', 'A G']  
X:1
L:1/4
M:6/4
K:D
|: B A G F- F/E/ D | f e d e E2 | B A G F- F/E/ D | f e d/c/ d D2 ::[M:3/4] B A G | 
[M:3/2] F A G B A c/d/ |[M:3/4] e E2 |[M:3/4] B A G |[M:3/2] F A G B A B/c/ |[M:3/4] d D2 :: 
[M:6/4] f g a f- f/e/ d | f e d c e2 | f g a f- f/e/ d | f e d/c/ d D2 :|  