Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
Q:1/4=140
M:2/4
K:G
['df df dB', 'a/g/f/e/ dB']  
X:1
L:1/8
Q:1/4=140
M:2/4
K:G
 df df | dB B2 | d/e/f/e/ d/e/f/e/ | ge e2 | df df | dB g2 |{c} BA/G/ Af | ge e2 :: a>b a/g/f/e/ | 
 dB B2 | a>b ag/f/ | ge ef/g/ | a>b a/g/f/e/ | dB g2 |{c} BA/G/ Af | ge e2 :|  