Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/2
K:D
['F3 A F3 defa g2 fe dcdB', 'd2 faag f2 fe dcdA BAFA e']  
X:1
L:1/8
M:2/2
K:D
 D F3 A F3 | defa g2 fe | dcdB AFAB | defd e2 Bc | d F3 A F3 | defa g2 fe | dcdB ABdf | 
 afeg fd d2 :: faag f2 fe | dcdA BAFA | e g3 b g3 | a f3 ge e2 | D F3 A F3 | defa g2 fe | 
 dcdB ABdf | afeg fd d2 :|  