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Thursday, 2 May 2019

Frames in Artificial Intelligence

What is a Frame ?

A frame is a prototype of a concept
- Denoting the attributes of the concept
- The class of objects or concepts to which the concept in question belongs
And some more things ........

An instance of a frame is a representation of a SPECIFIC object
Instantiation of a frame




Example
  • Fido is a dog
  • The concept dog
  • Fido is a particular dog
  • How can we represent the concept/notion of the creature "dog"?



Dog
 {
         is a : mammal;
         no._of_legs: 4;
         type_of_teeth: sharp;
         has_tail: yes;
         color_of_skin:   ;
         owner:               ;
          .
          .
          .
 }

Fido
{
         is a: Dog;
         no._of_legs: 4;
         type_of_teeth: sharp;
         has_tail: yes;
         color_of_skin: Black;
         owner: Rahim;
         .
         .
 }


Object-Attribute-Value <o,a,v>
  • An instance of a frame denotes an object
  • A Frame denotes a class to which the object belongs
  • The slots denote the attributes of the object
  • The slots can be of different types
  • The slots are instantiated with values

Semantic Net to Frame



Slots
  • Slots denote attributes
  • Attributes are typed
  • Some values are defined in the frame definition (already instantiated)
  • Some values are defined in the instances only
  • Instantiated slots define facts - may be used to answer queries


What are there in a slot ?
  • Values
  • Types
  • Constraints over possible values
  • Predicates
  • Daemons/function
  • Compare with object oriented systems
  • Slots can be structured - frames within slots - pointers to frames

Predicates in a Slot

Two types in general
  • If needed
  • If added
If needed predicates state how to find/compute a value

If added predicates are used to check constraints on the values
  • Can be used for consistency checking as well.
Generic Values
  • Does Tom drink milk ?
  • The answer is not in the instance description og Tom.
→ Tom is an instance of a Boy
→ Also, Boy is a Human Being
In the description of Human Beings, we have "Human Beings drink milk"
All human beings drink milk.
The answer can therefore be INHERITED
Generic values are values which will hold true for all subclasses of the class and all instances of the class.
Hence, the generic values can be inherited down the hierarchy.
Tom has a pen . Does he need ink ?

Default Value
  • With which hand does Tom write ?
  • Again the answer is not in the description of Tom.
  • Since we are not told that Tom is left handed , we will assume that Tom writes with right hand.
  • Again inheritance of the Default Value

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