Page 79 - DCAP506_ARTIFICIAL_INTELLIGENCE

Unit 5: Knowledge Representation

Resolution Rule: Key Idea Notes

1. Consider A B and ¬ B  C
(a) if B is True, ¬ B is False and truth of second formula depends only on C
(b) if B is False, truth of first formula depends only on A
2. Only one of B, ¬ B is True, so if both A B and ¬ B  C are True, either A or C is

True, i.e., A  C is True
Hence the resolution rule is sound.

Task Make distinction between Conjunctive Normal Form (CNF) and Disjunctive Normal
Form (DNF).

5.4.3 Applying Resolution

1. The resolution rule is sound (resolving entailed by two parent clauses)
2. How can we use the resolution rule?

(a) Convert knowledge base into clausal form
(b) Repeatedly apply resolution rule to the resulting clauses
(c ) A query A follows from the knowledge base if and only if each of the clauses in the
CNF of A can be derived using resolution.

Self Assessment

Fill in the blanks:
12. A ........................... is a propositional letter or the negation of a propositional letter.
13. Resolution is considered as a basis of ........................... method.

5.5 Unification Algorithm

In Artificial Intelligence there is the question whether we should pursue “unified architectures
of cognition”. Those of us who build AI systems know that some amount of unification happens
automatically as a consequence of trying to simplify what we are building by making the
components general and reusable through building libraries, languages, and architectures. And
clearly that there has to be something better than Lisp!
Our feeling is that a total unification is not possible, but there is a strong reason why people
believe it is. To put it simply, everyone has a different idea of what it means to be intelligent,
that is, they have different beliefs about what kinds of problems are interesting or hard. This set
of “interesting problems” is usually far smaller than the set of problems people actually solve,
and so as a consequence unification may be possible for that small set. But when applied to
problems outside that set, the unification begins to break down and a great deal of additional
machinery is needed, defeating the original simplification.

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