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Default Reasoning

Default Reasoning. Q : How many wheels does John’s car have? A : Four (by default) The conclusion is withdrawn if one is supplied with the information that one wheel of John’s car has just been stolen. non-monotonicity. Default Reasoning. Q : Can bird Tweety fly? A : Yes (by default)

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Default Reasoning

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  1. Default Reasoning Q: How many wheels does John’s car have? A: Four (by default) The conclusion is withdrawn if one is supplied with the information that one wheel of John’s car has just been stolen.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 A: Yes (by default) The conclusion is withdrawn if it is added that Tweety is a penguin.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 John’s car have? A: Four (by default) The conclusion is withdrawn if one is supplied with the information that one wheel of John’s car has just been stolen.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 A: Yes (by default) The conclusion is withdrawn if it is added that Tweety is a penguin.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 John’s car have? A: Four (by default - CWA) The conclusion is withdrawn if one is supplied with the information that one wheel of John’s car has just been stolen.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 A: Yes (by default - CWA) The conclusion is withdrawn if it is added that Tweety is a penguin.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 Nixondiamond 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Da iff ais 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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