Develop a musical piece employing the provided motif and an alphabet-based structure.
X:1
L:1/8
Q:1/4=120
M:3/4
K:G
['D2 G>G B>B d>d b2 g2 (3gfg', "(3gfg a2 c'2 (3fef", 'D2 (3GDG (3BGB g2 z']  
X:1
L:1/8
Q:1/4=120
M:3/4
K:G
 D2 | G>G B>B d>d | b2 g2 (3gfg | a2 c'2 (3fef | g2 b2 D2 | G>G B>B d>d | b2 g2 (3gfg | 
 a2 c'2 (3fef | g4 :: (3gfg | a2 c'2 (3fef | g2 b2 (3gfg | a2 c'2 (3fef | g2 b2 (3gdB | 
 G>G B>B d>d | b2 g2 (3gfg | a2 c'2 (3fef | g4 :|"^Variation, followed by another AGG" D2 | 
 (3GDG (3BGB (3dBd"_etc" g2 z z |]  