Similar to the Bayesian case for the estimation of a single parameter, using the Bayesian framework requires us to specify the joint distribution for all the data instances and unknown parameters.
For the parameters we are trying to estimate, if we decide to have the parameters priori independent (which may not be applicable in all cases), then calculating the posterior becomes easier (which is analogous to likelihood decomposition in MLE). If we have a network comprising two nodes (), then we can calculate the posterior of independently of the posterior over , and the same decomposability can be generalized to larger networks.