Alternate Representational Methods CS 531: LUMS Lahore Dr. M M Awais Frames Graphical Representation: Semantic Nets

2 FOL CS 331/531 Dr M M Awais Approaches: Symbolic Symbolic All birds fly  X(bird(X) flies(X)) Problem (Commonsense/uncertain things are hard to represent through symbolic methods) Such as ‘Probably birds can fly’

3 FOL CS 331/531 Dr M M Awais Frames and Semantic Networks Provides a natural way of representing FACTUAL knowledge Knowledge is represented as collection of OBJECTS and RELATIONS We have CLASSES, SUBCLASSSES, and INSTANCES Class: the main branch of objects (such as animals is a class of living beings) Subclass: sub branch of the main class (birds) Instances: (crow, sparrow……..)

4 FOL CS 331/531 Dr M M Awais Semantic Networks/Frames Conceptual Description Language Instance (object, class) Subclass(class, superclass) Features(class, attribute, value) Superclass: Animal Subclass: reptiles and mammals, mammals have head Subclass of mammals: elephants (with size large and colour grey) Instances: Elephant A and B, B likes grass

5 FOL CS 331/531 Dr M M Awais Alternative Representation Use labels for the links that are similar to DFD in Software Engineering/Databases We have slot values to fill in Objects have Its super class/ class/ or subclass values Its specific properties

6 FOL CS 331/531 Dr M M Awais 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)

7 FOL CS 331/531 Dr M M Awais Example Problem:Animals 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 B: instance:Elephant eats:oranges Reptiles: subclass: Animal objects Slot values

8 FOL CS 331/531 Dr M M Awais 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 slot_value(C,P ) and return this value Otherwise, fail O=object, P=Attribute/Property slot_value(O,subclass) checks for slot value: subclass in O slot_value(O,instance) checks for slot value: instance in O

9 FOL CS 331/531 Dr M M Awais Example of the Algo. Question 1: What does elephant A likes? Step one: O = elephant A, P=likes Evaluate: slot_value(A,likes) returns: bananas query successful Mammal: subclass: Animal has_part: head Elephant:: subclass: Mammal color:grey size:large A: instance:Elephant likes:bananas B: instance:Elephant eats:oranges

10 FOL CS 331/531 Dr M M Awais Example of the Algo. Question 1: What is the color of the elephant A ? Step one: O = elephant A, P=color Evaluate: value(A,color) returns: nil query not successful Step Two: O=A, P=subclass/instance Evaluate: slot_value(A,subclass) returns: nil (A does not have slot value for a subclass) Evaluate: slot_value(A,instance) returns: Elephant Evaluate: slot_value(Elephant, colour) returns grey Mammal: subclass: Animal has_part: head Elephant:: subclass: Mammal color:grey size:large A: instance:Elephant likes:bananas B: instance:Elephant eats:oranges

11 FOL CS 331/531 Dr M M Awais Default and Multiple Inheritance 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 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 owner:Farid 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.

12 FOL CS 331/531 Dr M M Awais 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 rectangle or ellipse) Links (or arcs): represent the relationship between the elements. Shown as vector from one element to the other element

13 FOL CS 331/531 Dr M M Awais Examples Shahid eats apple Nodes: shahid and apple Link: eating Shahideatsapple [shahid eats apple] 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 BINARY RELATION (examples of binary relation IS_A, PART_OF etc.)

14 FOL CS 331/531 Dr M M Awais Examples, cont… Hassan is a mammal Nodes: hassan and mammal Link: isa Hassanisamammal [hassan is_a mammal] Horse has a tail Tail partof Horse [tail part_of horse]

15 FOL CS 331/531 Dr M M Awais Examples, cont… Horse is a mammal with tail TAIL HORSEMAMMAL partof isa Could use an ellipse instead of rectangle

16 FOL CS 331/531 Dr M M Awais 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 TAIL HORSE MAMMAL partof isa BLACKTONY color instance

17 FOL CS 331/531 Dr M M Awais 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 HORSE MAMMAL partof isa BLACKTONY color instance

18 FOL CS 331/531 Dr M M Awais Examples, cont… Problem:Animals have types reptiles and mammals. All Mammals have heads. Elephant 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

19 FOL CS 331/531 Dr M M Awais Examples, cont.. ANIMAL REPTILES MAMMALSHEAD ELEPHANT GREY LARGE A BORANGES BANANAS subclass eats has_part size color likes instance All relations have to be defined

20 FOL CS 331/531 Dr M M Awais 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.

21 FOL CS 331/531 Dr M M Awais 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.