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
['G,B,DB, CB,A,B, CDEF', 'g2 dB']  
X:1
L:1/8
M:2/2
K:G
 G2 DB, G,B,DB, | CB,A,B, CDEF | G2 DB, G,B,DF | Ggdc BcAF | GGDB, G,B,DB, | CB,A,B, CDEF | 
 GFGf (3(gfe) dc | (3(Bcd) Ac BG G2 || g2 dB GBdf | gbag fdef | g2 dB GBdB | cBAG FGAd | 
 gedB GBdf | gbag fgag | (3(bag) (3(agf) (3(gfe) dc | (3(Bcd) AG FDEF"_D.C." |]  