In rough set theory with every decision rule two conditional probabilities,
called certainty and coverage factors, are associated. These two factors a
re closely related with the lower and the upper approximation of a set, bas
ic notions of rough set theory. It is shown that these two factors satisfy
the Bayes' rule.
The Bayes' rule in our case simply shows some relationship in the data, wit
hout referring to prior and posterior probabilities intrinsically associate
d with Bayesian inference. This relationship can be used to "invert" decisi
on rules, i.e., to find reasons (explanation) for decisions thus providing
inductive as well as deductive inference in our scheme.