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Wednesday, 1 May 2019

Reasoning in Semantic Net of Artificial Intelligence

Relating Entities

Representing the height of two people :




Comparing the heights of two people :




We need extra nodes for the concept as well as its value.

Inheritance

AI researchers have refined the notion of inheritance : It is called a specialized inferencing technique

"for representing properties of classes, exceptions to inherited properties, multiple superclasses, and structured concepts with specific relations among the structural elements"

Reasoning in Semantic Net
  • Semantic nets allow you to define relations between objects, including class relations (X is a Y).
  • Only restricted inference supported by the methods - that based on inheritance .
  • So... Fido is a dog, dogs have 4 legs, so Fido has 4 legs.
Semantic Networks :



By traversing networks we can find :
  • That Nellie has a head (by inheritance)
  • That certain concepts related in certain ways (e.g., apples and elephants).
BUT : Meaning of semantic networks was not always well defined.
  • Are all Elephants large, or just typical elephants?
  • Do all Elephants live in the "same" Africa?
  • Do all animals have the same head?
For machine processing these things must be defined.

Default and Generic Properties

Generic Properties are always inherited
    Fido is a dog
    dog is a animal
Hence Fido is a animal

This is true because all dogs are animals 


Default
  • If nothing is known to the contrary inherit the value
  • Fido is a dog
  • dog has part tail
  • If we do not have any information that Fido's tail has been chopped off
  • Fido has part tail

Superseding default values
  • If we know more details in a subclass or in an instance the default value inherited is overwritten
  • bird can fly
  • Ostrich is a bird By default we infer Ostrich can fly 
  • But
           - If at the ostrich subclass we know that it cannot fly then we modify the inherited inference to Ostrich cannot fly

Semantic Net Inference

To find the value of attribute a for object o :
  1. Set a list L to contain the node corresponding to o.
  2. Set the current node to be the next node from L.
  3. f there is an arc labeled a - it points to the answer.
  4. Otherwise -add to L all nodes pointed to by Instance or Subclass arcs coming from the current node.
  5. If L is not empty go to step 2.

What is the hair colour of Marcus ?

Multiple Inheritance

What if an object the same attribute from two different classes ?




Inference Technique Options
  • To deal with multiple inheritance we need to add something to determine which class takes precedence.
  • In general we want the most specific class to be used.
         - Could simply use path length
         - The notion of inferential distance has also been explored

There can always be problems


Is Rita confident or shaky ?

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