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
['G3 B', 'ag f2']  
X:1
L:1/8
M:4/4
K:G
 G3 e dGBd | edBe dB A2 | G3 B dG (3Bcd | AE E2 GE D2 | G3 B d2 Bd | edcB cdeg | edcB cd e2 |1 
 gedB AGEF :|2 gedB agef |: g3 b ag f2 | edBe dG (3Bcd | g2 gb ag f2 | eaag agef | g2 bg ag f2 | 
 edBe dG (3Bcd | edcB c2 ef |1 gedB ag e2 :|2 gedB AGEF ||  