Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:D
['DDD FDD FDF ECE DDD FEF', 'DAF DAF', 'B/c/dB c2 c', 'dAF dAF', 'dAF def', 'z AF']  
X:1
L:1/8
M:6/8
K:D
 DDD FDD | FDF ECE | DDD FEF | AGF ECE :: DAF DAF | DAF ECE | DAF DAF | AGF ECE :: B/c/dB c2 c | 
 B/c/dB c2 c | B/c/dB c2 c | AGF ECE :: dAF dAF | dAF BGE | dAF dAF | ECE GFE :: dAF def | 
 dAF BGE | dAF def | dAF BGE :| z AF AFA | z BG BGB | z cA cAc | z dB dBd | z dB z cA | z BG z AF | 
 z GE z FD | ECE GFE ||  