Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:3/4
K:G
['B AG A3 B cB c2 e2']  
X:1
L:1/8
M:3/4
K:G
 D2 | GF G3 B | AG A3 B | cB c2 e2 | B2 B2 D2 | GF G3 B | AG A3 B | cB c2 e2 | B2 B2 z G | 
 Bc d3 B | cd e3 e | de d3 B | AG A3 B | cB c2 e2 | B2 B3 G | Bc d3 B | cd e3 e | de d3 B | 
 AG A3 B | cB c2 e2 | B2 B2 |]  