Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:4/4
K:D
['g fdec dcAg fdec d2 de fdec', 'AD (3EFG AB =cA G2 Addc d3']  
X:1
L:1/8
M:4/4
K:D
 g | fdec dcAg | fdec d2 de | fdec dBAB | =cAGE D3 g | fdec dcAg | fdec d2 de | fdec dBAB | 
 =cAGE D2 AD || (3EFG AB =cA G2 | Addc d3 e | fdec dBAB | =cAGE D2 AD | (3EFG AB =cA G2 | 
 Addc d3 e | fdec dBAB | =cAGE D3 ||  