Create a composition by utilizing the given alphabet-based musical pattern and the provided melodic theme.
X:1
L:1/8
M:4/4
K:G
['Bc dcBA Bgfg e4 d4 cdcB ABAG', 'g2 bg e2 ag f4']  
X:1
L:1/8
M:4/4
K:G
 Bc | dcBA Bgfg | e4 d4 | cdcB ABAG | F4 D4 | DEFG A2 B2 | c2 de d2 c2 | BAGA E2 F2 | G6 :| d2 | 
 g2 bg e2 ag | f4 d4 | g2 bg e2 ag | f4 d2 ef | gddd gddd | gdgd gddd | g2 f2 edcB | ABAG F2 E2 | 
 DEFG A2 B2 | c2 de d2 c2 | BAGA E2 F2 | G6 :|  