Lecture 6 Knowledge Representation NonFormal Method Semantic Nets Frames

1
Lecture 6Knowledge RepresentationNon-Formal
Method Semantic Nets Frames

2
Semantic Nets

• A semantic network focuses on the graphical
  representation of relations between elements in a
  domain.
• Components are nodes and links
• Nodes used to represent domain elements
• (normally represented with rectangles and in some
  books with ellipse)
• Links (or arcs) represent the relationship
  between the elements. Shown as vector from one
  element to the other element

3
Examples

• Hassan eats meat
• Nodes hassan and meat
• Link eating
• Hassan eats Meat
• Link can be viewed as something that asserts to
  be true about one element relative to another. An
  assertion can only be true or false, therefore
  fundamentally its BINAR RELATION
• (examples of binary relation ISA, PART OF etc.)

4
Examples, cont..

• Hassan isa mammal
• Nodes hassan and mammal
• Link isa
• Hassan isa mammal
• Horse has a tail
• Tail partof Horse

5
Examples, cont..

• Horse is a mammal with tail

TAIL
partof
isa
HORSE
MAMMAL
6
Examples, cont..

• Instance a specific example of a class is the
  instance of that class.
• Animals are a class of living beings. Humans are
  subclass of animals and Zahra is an instance of
  subclass human, class animals
• Horse is a mammal with a tail. Tony is horse of
  black color

7
Examples, cont..

• Property Inheritance The properties of the class
  are inherited by the instances by default, unless
  specified.Tony in the example below also has a
  tail.

TAIL
partof
isa
HORSE
MAMMAL
instance
color
BLACK
TONY
8
Examples, cont..

• ProblemAnimals have types reptiles and mammals.
  All Mammals have heads. Element is a typical
  mammal with grey color and large size. A and b
  are two elephants. A likes bananas and and B eats
  oranges.
• Nodes Animals, reptiles, mammals, elephants, A,
  B, bananas and oranges

9
Examples, cont..

• ProblemAnimals have types reptiles and mammals.
  All Mammals have heads. Element is a typical
  mammal with grey color and large size. A and b
  are two elephants. A likes bananas and and B eats
  oranges.

color
instance
likes
10
Examples, cont..

• Problem
• Vertebrates are animals with several types. Birds
  are type of vertebrates with feathers. Using
  these feathers they can fly. A bluebird is
  typical bird with blue colour and small size.
  Horses are also vertebrates, but are mammals.
  They have tails and cannot fly. Trigger is a
  horse with white colour. This horse is very old
  and is nearly dead.

11
Examples, cont..
12
Examples, cont..

• Problem
• Snow is form of water, it is soft, slippery and
  white in color. Ice is also formed of water and
  share all the properties of snow except that it
  is hard and clear. One can form snowman from ice
  frosty is a snow man that I saw in the forest.

13
Frames

• Frames are a variant of semantic networks, and a
  popular way to represent facts in expert systems
• Relevant information is stored in single complex
  entity called frames
• Frames support inheritance, superficially similar
  to data structure (struct)

14
Example

• ProblemAnimals have types reptiles and mammals.
  All Mammals have heads. Element is a typical
  mammal with grey color and large size. A and b
  are two elephants. A likes bananas and and B eats
  oranges.

Mammal subclass Animal has_part
head Elephant subclass Mammal color grey
size large A instance Elephant likes bananas

Reptiles subclass Animal
objects
Slot values
15
Default and Multiple Inheritance
Default values are those values that can be
overridden and changed for subclass and/or
instances
Multiple Inheritance When more than one parent
class is present, which attribute is to be passed.

• Mammal
• subclass Animal
• has_part head
• warm_blooded yes
• angry yes
• Elephant
• subclass Mammal
• has_trunk yes
• color grey
• size large
• habitat jungle
• Circus_Animal
• subclass Animal
• habitat tent
• skills balancing on a ball
• A
• instance Circus_Animal
• Elephant
• color pink

• Mammal
• subclass Animal
• has_part head
• warm_blooded yes
• angry yes
• Elephant
• subclass Mammal
• has_trunk yes
• color grey
• size large
• angry no
• A
• instance Elephant
• color pink
• owner Farid
• likes bananas
• B instance Elephant
• size small

?
16
Implementing Simple Frames

• IF slot_value (O,P) returns a value V, return V.
• Otherwise, IF slot_value(O,subclass)
• or
• slot_value(O,instance)
• return C,
• find value(C,P )
• and return this value
• Otherwise, fail

Oobject, PAttribute/Property slot_value(O,subcla
ss) checks whether O is a subclass or
not slot_value(O,instance) checks whether O is a
instance or not
17
Example of the Algo.

• Question 1 What does elephant A likes?
• Step one O elephant A, Plikes
• Evaluate value(A,likes)
• returns bananas ------------query successful

18
Example of the Algo.

• Question 1 What is the color of the elephant A ?
• Step one O elephant A, Pcolor
• Evaluate value(A,color)
• returns nil ------------query not successful
• Step Two
• Evaluate slot_value(A,subclass) returns nil A s
  not subclass
• Evaluate slot_value(A,instance) returns Elephant
• Evaluate slot_value(Elephant, colour) returns
  grey

19
Example
DEVELOP A FRAME FOR A CAR
20
Example CAR FRAME