Create a composition by utilizing the given alphabet-based musical pattern and the provided melodic theme.
X:1
L:1/4
M:3/4
K:G
['G D2 D']  
X:1
L:1/4
M:3/4
K:G
 D | G3/2 A/ _B | A _B A | G F G | D2 D | G2 A | d3/2 e/ d | c B A- | A z B/A/ | G G d/^c/ | 
 d d G/G/ | G3/2 F/ G | D2 D | G A d- | d2 c/B/ | A3/2 B/ A | G2 |]  