Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/2
K:G
['g2 dg Bgdg', 'Bc/d/ dB']  
X:1
L:1/8
M:2/2
K:G
 d | g2 dg Bgdg | Bgdg a2 ab | g2 dg Bgdg | DAFD G2 G :| c | Bc/d/ dB cd/e/ ec | Bc/d/ dB A2 Ac | 
 Bc/d/ dB cd/e/ ec | dgfa g2 gc | Bc/d/ dB cd/e/ ec | Bc/d/ dB A2 Ac | BdBd cece | dgaf g2 g ||  