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Default Reasoning

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The conclusion is withdrawn if it is added that Tweety is a penguin. non-monotonicity ... penguin(x) abnormal(x) 7. Default Reasoning. Usually, Quakers are pacifist ... – PowerPoint PPT presentation

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Title: Default Reasoning


1
Default Reasoning
  • Q How many wheels does Johns car have?
  • A Four (by default)
  • The conclusion is withdrawn if one is supplied
    with the information that one wheel of Johns car
    has just been stolen.

non-monotonicity
2
Default Reasoning
  • Q Can bird Tweety fly?
  • A Yes (by default)
  • The conclusion is withdrawn if it is added that
    Tweety is a penguin.

non-monotonicity
3
Default Reasoning
  • Q How many wheels does Johns car have?
  • A Four (by default)
  • The conclusion is withdrawn if one is supplied
    with the information that one wheel of Johns car
    has just been stolen.
  • car(x) ? ? wheel-num(x, 4)

4
Default Reasoning
  • Q Can bird Tweety fly?
  • A Yes (by default)
  • The conclusion is withdrawn if it is added that
    Tweety is a penguin.
  • bird(x) ? ? fly(x)

5
Default Reasoning
  • Q How many wheels does Johns car have?
  • A Four (by default - CWA)
  • The conclusion is withdrawn if one is supplied
    with the information that one wheel of Johns car
    has just been stolen.
  • car(x) ? ?abnormal(x) ? wheel-num(x, 4)
  • wheel-stolen(x) ? abnormal(x)

6
Default Reasoning
  • Q Can bird Tweety fly?
  • A Yes (by default - CWA)
  • The conclusion is withdrawn if it is added that
    Tweety is a penguin.
  • bird(x) ? ?abnormal(x) ? fly(x)
  • penguin(x) ? abnormal(x)

7
Default Reasoning
  • Usually, Quakers are pacifist
  • Usually, Republicans are not pacifist
  • Richard Nixon is both a Quaker and a Republican
  • Q Is Nixon a pacifist?

8
Default Reasoning
  • Usually, Quakers are pacifist
  • Usually, Republicans are not pacifist
  • Richard Nixon is both a Quaker and a Republican

pacifist
Nixon diamond
Quaker
Republican
Nixon
9
Default Reasoning
  • Usually, Quakers are pacifist
  • Usually, Republicans are not pacifist
  • Richard Nixon is both a Quaker and a Republican
  • quaker(x) ? ?abnormal1(x) ? pacifist(x)
  • republican(x) ? ?abnormal2(x) ? ?pacifist(x)
  • quaker(Nixon)
  • republican(Nixon)

10
Default Reasoning
  • Default consequence
  • KB ??D a
  • iff a is true in every preferred model of KB.

11
Default Reasoning
  • quaker(x) ? ?abnormal1(x) ? pacifist(x)
  • republican(x) ? ?abnormal2(x) ? ?pacifist(x)
  • quaker(Nixon)
  • republican(Nixon)

Model 2
Model 1
quaker(Nixon) republican(Nixon) ?abnormal1(Nixon)
abnormal2(Nixon)
quaker(Nixon) republican(Nixon) abnormal1(Nixon)
?abnormal2(Nixon)
more preferred to
12
Default Reasoning
  • Uncertain reasoning
  • car(x) ? wheel-num(x, 4) l1, u2
  • bird(x) ? fly(x) l3, u4
  • quaker(x) ? pacifist(x) l5, u6
  • republican(x) ? ?pacifist(x) l7, u8
  • l, u probabilistic or possibilistic intervals
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