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Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

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A common question that may be raised is why to use --> <strong>and</strong> /--><br />

operators, when there exist monotonic <strong>and</strong> / operators. The answer to<br />

this is that the --> <strong>and</strong> -/--> operators can avoid contradiction, which is not<br />

possible with <strong>and</strong> / .<br />

The following example illustrates how the contradiction that arises due<br />

to use of <strong>and</strong> / only can be avoided by employing ---> <strong>and</strong> -/-->.<br />

Example 8.3: Consider the symantic net shown in fig 8.9. Here, by<br />

inheritance we have<br />

Next, we have<br />

Tweety(X) Bird(X) Has-wings(X) Fly(X) <strong>and</strong> thus<br />

Tweety(X) Fly(X).<br />

Tweety(X) Diseased (X) /Fly(X)<br />

i.e., Tweety(X) /Fly(X) .<br />

So, we find a contradiction:<br />

Tweety(X) Fly(X) <strong>and</strong><br />

Tweety(X) /Fly(X) .<br />

This contradiction, however, can be avoided if we use ---> operator as<br />

shown in fig 8.10. Here, Has-wings(X) --> Fly(X) denotes that it is a default<br />

property that anyone having wings should fly. But the specialized property<br />

states that<br />

Diseased(X) / Fly(X)<br />

or, Diseased(X) ¬Fly(X).<br />

Since specialized property should be given importance, we infer<br />

Tweety(X) ¬Fly(X).

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