Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:4/4
K:Eb
['B e2 BA GEBG F (f2 e)', 'agfa g']  
X:1
L:1/8
M:4/4
K:Eb
 B | e2 BA GEBG | F (f2 e) fccd | eBGB AcBg | agfa ge e :| g | bgeg egbg | afge d (f2 g) | 
 bgeg gebg | agfa g (e2 g) | bgeB eBGE | GEB,E (DF) F2 | EB,EB GeBg | agfa g e2 ||  