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:Bb
['f2 gg/d/']  
X:1
L:1/8
M:2/4
K:Bb
 gg/f/gb | g>fdc/d/ | f4 | cb/c/dc | b4 | gg/f/gb | gg/f/d/f/c/d/ | f4 | gcc/b/G | f2 gg/d/ | f4 | 
 cb/c/dc | b3 g | cb/c/dc | b3 g | gfgb | gfdc/d/ | f4 | gc/d/c/b/g | f2 gg/d/ | f4 | ggdd | ggdd | 
 dd/f/bg | f4 | bbbd | c>df>g | b4 | d>fbg | f2 gg/d/ | f4 |]  