Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:6/8
K:G
['B3 dBA AGE DEG BAB cBc', 'b2 g gfg']  
X:1
L:1/8
M:6/8
K:G
 A | B3 dBA | AGE DEG | BAB cBc | deB dBA | B3 dBA | AGE DEG | BAB cBc | dBG G2 :| a | b2 g gfg | 
 agf efg | b2 g gfg | deB dga | b2 g gfg | agf efg | bd'b c'af | gba g2 :|  