Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:2/4
K:G
['d2 b>a b b2 z a2 b>d']  
X:1
L:1/8
M:2/4
K:G
 d2 b>a | b b2 z | a2 b>d | b>ag>e | g3 a | bbg>b | ag e2 | d3 z | dB d2 | eg z2 | gge>d | B3 z | 
 a a2 d | b2 g2 | ee g2 | g3 z |]  