Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/4
Q:3/4=90
M:6/4
K:Gmin
['b a g', 'd c B']  
X:1
L:1/4
Q:3/4=90
M:6/4
K:Gmin
 g | g ^f g d g f | g3 a3 | b a g b a g | ^f3 d2 c | B e d A d c | G B A ^F G A | B c d (c2 B/c/) | 
 d3- d2 :| d | B c d d c B | f3- f2 f | g f e d c B | A3- A2 f | g2 z f2 z | e2 z d2 z | 
 c b d c2 B | B3- B2 c | d e f f d e | e3 z z"^NB" =e | e f g g a g | ^f3- f2 f | g3 f3 | e3 d3 | 
 c e d A2 G | G3- G2 |]  