CSE4108
Artificial Intelligence Lab
Spring 2015
Session 1
Topic 1. Logic Programming and Backward Chaining.
A simple knowledgebase (KB) from the Kinship Domain
Object relationships:
Hasib is a parent of Rakib. Rakib is a parent of Sohel. Rakib is a parent of
Rebeka. If X is a parent of Y and Y is a parent of Z, then X is a grandparent of Z.
Facts and Rules (KB) in ProLog:
parent (‘Hasib’ , ’Rakib’). parent(‘Rakib’ , ’Sohel’). parent(‘Rakib’ , ’Rebeka’).
grandparent (X, Z) :- parent(X, Y), parent(Y, Z).
[2 2-place predicates; 3 variables; full stop (.) as the end marker of a clause/
sentence / statement; :- as ‘if’; comma (,) as logical AND. ]
Queries to KB and Backward Chaining:
Is Hasib a grandparent of Rebeka?
grandparent (‘Hasib’, ‘Rebeka’).
-
-
Is Hasib a parent of a person and that person is a parent of Rebeka?
parent (‘Hasib’, X), parent(X, ‘Rebeka’).
parent (‘Hasib’, ‘Rakib’).
[X ← Rakib]
Is Rakib a parent of Rebeka?
parent (‘Rakib’, ‘Rebeka’).
Yes.
√ Various types of queries are possible.
[Who is a parent? ‘parent (X, _).’ Who has a parent? ‘parent (_, X).’ Who is a parent
and who has a parent? ‘parent (X, _), parent (_, X).’ Who is a parent or who has a
parent? ‘parent (X, _); parent (_, X).’]
√ Various rules may also be formulated.
√ Nesting of the following type should be avoided.
greatGrandParent (X, Z) :- parent(X, Y), grandparent(Y, Z).
greatGreatGrandParet(X, Z) :- parent(X, Y), greatGrandParent(Y,Z),.
Topic 2. Logic Programming and Recursion.
i)
Ancestor
a. A parent is an ancestor.
b. A parent of an ancestor is an ancestor.
[X is an ancestor of Y, if X is a parent of an ancestor of Y.]
------------------------ancestor(X, Y) :- parent(X, Y).
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y).
ii) Factorial of 0 is 1.
If n is greater than 0, then factorial of n is the product of n and the factorial of n-1.
[Factorial of N is F, if N is greater than 0 and F is the product of N and factorial of N-1.]
----------------------factorial(0, 1).
factorial(N, F) :- N>0, N1 is N-1, factorial(N1, F1), F is N*F1.
Exercise:
1) Enrich the KB discussed in Topic 1 with ‘brother’ and ‘sister’ rules. [Use not (X=Y) to avoid
reflexivity and 1-place predicate ‘male’ where necessary.]
2) Define a recursive procedure in English and in ProLog to find the sum of 1st n odd numbers.
3) Define a recursive procedure to find the sum of the 1st n terms of the following series.
100+105+110+…
4) Define a recursive procedure to find the sum of the 1st n terms of the following series.
10x11 + 11x13 +12x15 + …
5) Define a recursive procedure to find the sum of 1st n terms of an equal-interval series given the
1st term and the interval. [Use a 4-place predicate.]
6) Develop a KB that represents a simple directed weighted graph, and provides a way for finding
the length of a path between any two nodes. [Use three place predicates ‘neighbor’ and ‘path’.]