Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:2/4
K:Bb
['D GABc dG GA BB', 'd3 B/c/ dddd cc c2 BBBB AA']  
X:1
L:1/8
M:2/4
K:Bb
 D | GABc | dG GA | BB cc | d3 :: B/c/ | dddd | cc c2 | BBBB | AA AD | GABc | dG GA | 
 BA/G/ A/c/A/^F/ | G3 :|  