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
['G2 (GB) A2 (Ac) dBcA', 'g2 (ga) f2 (fg)']  
X:1
L:1/8
M:4/4
K:G
 G2 (GB) A2 (Ac) | dBcA GFED | G2 (GB) A2 (Ac) | dBcA G2 G2 :: g2 (ga) f2 (fg) | e2 (ef) agfe | 
 g2 (ga) f2 (fg) | egaf g2 g2 | g2 (ga) f2 (fg) | e2 (ef) agfe | g2 (Bd) e2 (Ac) | dBcA G2 G2 :|  