Logic Program

A logic program is a set of logical rules or clauses. Logic programs are employed to answer queries using the resolution inference rule. For example, consider the following logic program:

grandparent(X,Y) :- parent(X,Z),                     parent(Z,Y). parent(X,Y) :- father(X,Y). parent(X,Y) :- mother(X,Y). father(charles, william).     mother(diana, william). father(philip, charles).     mother(elizabeth, charles). father(john, diana).     mother(frances, diana).

Using resolution we obtain the following answers to the query :-grandparent(X,Y):

X = philip,         Y = william ; X = john,           Y = william ; X = elizabeth,    Y = william ; X = frances,       Y = william.

Cross-References

• Clause

• First-Order Logic

• Prolog