The problem with else is that it is hard to define what you mean by else. As put by Ernest Friedman (author of Jess):
+Nope, doesn't work that way, because there are several different kinds
of "not true" that might apply (facts don't exist; facts exist but
fields don't match; etc.) You have to write a separate rule for the
So the best bet is to express what you really mean as multiple rules.