Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:4/4
K:G
['GB B2', 'G2 Bd g3']  
X:1
L:1/8
M:4/4
K:G
 GB B2 cdeg | dBGA BA A2 | GB B2 cdec | dBGA BGGF | GB B2 cdeg | dBGA BA A2 | cBcd egfe | 
 dBGA BAGF :| G2 Bd g3 a | gedB de g2 | G2 Bd g3 d | egdB ABBA | G2 Bd g3 a | gedB dega | 
 babg agaf | gedB A2 BA :|  