How to define reasonable observed data

Questions
4

I mean there is no observed data. so may I run it with no observed data. if not, how to define the observed data?

x1=pm.Normal(‘x1’,mu=0.5,sd=0.5)

x2=pm.Normal(‘x2’,mu=0.5,sd=0.5)

y=x1+x2

Y=pm.Normal(‘Y’,mu = y,sd=1)