Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:2/2
K:G
['BG G2', 'Bd eB B2 gB B2 BAGB A2']  
X:1
L:1/8
M:2/2
K:G
 BG G2 AGFA | DG G2 A2 dc | BG G2 A3 B |1 BAAG ABdc :|2 BAAG A2 Bd || (3ege dB eB d2 | eBdB A2 Bd | 
 eB B2 gB B2 | BAGB A2 Bd | e3 d e2 ab | gedB A2 BA | G2 Bd g3 b | agef gedc ||  