Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['DD DD']  
X:1
L:1/8
M:4/4
K:D
 D | DD DD DD DD | ED CD E3 E | EE EE EE EE | FE DE F3 | F | FF FF FF FF | GF EF G3 G | 
 GG GG GG GG | AG FG A3 | D | Dd cB A3/2 G/ FA | A3/2 A/ GE D3 ||  