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 :

Set a list L to contain the node corresponding to o.
Set the current node to be the next node from L.
f there is an arc labeled a - it points to the answer.
Otherwise -add to L all nodes pointed to by Instance or Subclass arcs coming from the current node.
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