Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/16
M:2/4
K:Bb
['b2fe d2dc B2Bd F4 B2Bd', '[DB]4 c2ce d2dB c2ce d4 =efga bgeg']  
X:1
L:1/16
M:2/4
K:Bb
 b2fe d2dc | B2Bd F4 | B2Bd c2ce | d2f2 c2a2 | b2fe d2dc | B2Bd F4 | B2Bd cecA | B2cd [DB]4 :: 
 c2ce d2dB | c2ce d4 | =efga bgeg | f2ga f4 | b2fe d2dc | B2Bd F4 | B2Bd cecA | B2cd [DB]4 :|  