Page 99 - DCAP506_ARTIFICIAL_INTELLIGENCE

Unit 7: Symbolic Reasoning under Uncertainty

One general solution (consistent with PROLOG notation) is to demonstrate that fact P is accurate Notes
effort to prove P. If we do not succeed we may say that P is consistent (because P is false).
However assume the well-known set of assertions connecting to President Nixon.

 x: Republican(x) M Pacifist(x)  –Pacifist(x)
 x: Quaker(x) M Pacifist(x) Pacifist(x)
Now this specifies that Quakers is apt to be pacifists and Republicans tend not to be.
But Nixon was both a Quaker and a Republican and thus we could assert:

Quaker(Nixon)
Republican(Nixon)
This now leads to our total knowledge turning out to be inconsistent.

Default Logic

Default logic brings in a new inference rule:
A B

C
which specifies if A is deducible and it is consistent to presume B then conclude C.

Notes Now this is alike to Non-monotonic logic but there are a number of distinctions:
 New inference rules are utilized for calculating the set of probable extensions. So, in
the Nixon example above Default logic can assist both assertions as is does not say
anything regarding how to select between them — it will rely on the inference
being made.
 In Default logic any non-monotonic expressions are rules of inference rather than
expressions.

Self Assessment

Fill in the blanks:

4. In .............................. reasoning if we expand at set of axioms we cannot withdraw any
present declarations or axioms.
5. In .............................. reasoning, we want to sketch conclusion based on what is most probable
to be correct.
6. Non-Monotonic reasoning is common depiction of a class of .............................. .
7. .............................. is fundamentally an extension of first-order predicate logic to comprise
a modal operator, M.
8. Default logic brings in a new inference rule: .............................. which specifies if A is
deducible and it is consistent to presume B then conclude C.
9. .............................. and the conclusions we execute on it is an example of monotonic reasoning.

LOVELY PROFESSIONAL UNIVERSITY 93