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
['', 'f2 g2', 'f_e/f/ e/d/c']  
X:1
L:1/8
M:4/4
K:G
 d |: f2 g2 f_e/f/ _ed | f4- f_e/f/ ed | f2 g2 ag_ba | g4- gga_b | a2 g2 d'2 f2 | g4- gga_b | 
 aggf f_eed | f4- fd _e/d/c | c2 _b/a/g f_e/f/ _e/d/c |1 d6 z :|2 d8 || 
 (3f/g/f/d (3f/g/f/d f/g/a g/f/_e | d2 f2 a2 d'2 | (3f/g/f/d (3f/g/f/d f/g/a g/f/_e | d4 d'4 | 
 z d'c'_b agba | g8 | z c'_ba g=fag | =f8 | aggf f_eed | f4- fd_ed | aggf f_e/f/ e/d/c | 
 d2 f2 a2 d'2 | aggf f_e (3ede | f4- fd _e/d/c | c2 _b/a/g f_e/f/ e/d/c | d8 |]  