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
['', 'GBAG E4 DEGA', 'gedB A']  
X:1
L:1/8
M:2/2
K:G
 D2- |: DEGA B2 BA | GBAG E4 | DEGA BABA | GBAG E4 | DEGA B2 BA | GBAG E4 | DEGA B2 ef | 
 gedB A G3 :: [Bg]3 [Bg] [Bg]2 g2 | gaba ge d2 | !slide!g3 e gega | gedB A G3 | DEGA B2 BA | 
 GBAG E4 | DEGA B2 ef | gedB A G3 :|  