We doubt that Julius is a frog. It is highly likely that Jessica is a mouse. Chances are slight that Bernhard is gray. There is almost no chance that if 'Julius is a frog' or 'Bernhard is gray' or both then Mary moved to the office. There is little chance that if 'Jessica is a mouse and Julius is a frog' then Sandra left the milk. It is highly unlikely that if 'Jessica is a mouse and Julius is a frog' then Daniel got the milk.
Chances are slight that either 'Jessica is a mouse' or 'Daniel got the milk' but not both.
It is highly likely that either 'Jessica is a mouse' or 'Daniel got the milk' but not both.
Chances are slight that either 'Jessica is a mouse' or 'Daniel got the milk' but not both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.2::factA.
  0.9::factB.
  0.1::factC.
  %hop1
  0.02::factX:-or(factA,factC).
  0.1::factY:-and(factB,factA).
  0.05::factZ:-and(factB,factA).

  %hop2
  conclusion:-xor(factB,factZ).

  query(conclusion).
  
Either 'Jessica is a mouse' or 'Daniel got the milk' but not both.