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Ch7: Structured Knowledge Representation

Semantic nets

Frames

Conceptual graphs

Conceptual dependency

Slide 2Faculty of Computer Science and Engineering HCMUT

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Semantic Nets

The main ideas

For representing knowledge in structures

The meaning of a concept comes from the ways it isconnected to other concepts

Labelled nodes re resentin conce ts are connected

Slide 3Faculty of Computer Science and Engineering HCMUT

by labelled arcs representing relations

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Semantic Nets

Mammal

Person Noseisa

instance

has-part

Slide 4Faculty of Computer Science and Engineering HCMUT

Use inheritance: has-part(Owen, Nose)

OwenRed Liverpool

color team

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Semantic Nets

Intersection Search (Quillian, 1968):

To find relationships among objects

Spreading activation out from each of two nodes andseeing where the activation met

M mm l

Slide 5Faculty of Computer Science and Engineering HCMUT

What is the connection between Liverpool and Red?

Person

Owen

Nose

Red Liverpool

isa

instance

has-part

uniform

color team

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Semantic Nets

Mammal

isa

-

Unary predicate

Binary predicate

Presenting the predicates:

Slide 6Faculty of Computer Science and Engineering HCMUT

Person

Owen

Nose

Red Liverpool

instanceuniformcolor team

person(Owen) instance(Owen, Person)

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Semantic Nets

John gives Mary a book

Give Book

Three or more place predicate

Slide 7Faculty of Computer Science and Engineering HCMUT

John gagent

binstance instanceobject

Mary

beneficiary

give(John, Mary, book)

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Semantic Nets

John 1.8height

John Bill

H1 H2greater-than

height height

Making Some Important Distinctions

Slide 8Faculty of Computer Science and Engineering HCMUT

John

H1 H2

height

Bill

heightgreater-than

1.8

value

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Semantic Nets

The dog bit the mail-carrier

Dogs Bite Mail-Carrier

Partitioned Semantic Nets

Slide 9Faculty of Computer Science and Engineering HCMUT

d b m

instance instance instance

victimassailant

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Semantic NetsEvery dog has bitten a mail-carrier

d b m

Dogs Bite Mail-Carrier

instance instance instance

victimassailantS1

g

GS

instance

form

Slide 10Faculty of Computer Science and Engineering HCMUT

Every dog has bitten the mail-carrier in town

Dog

d b

instance

Bite

assailant

Mail-Carrier

m

instance instance

victimg

GS

instance form

S1

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Semantic Nets

Every dog has bitten every mail-carrier

Dogs Bite Mail-Carriers

instance instance instance

victimassailantS1

Slide 11Faculty of Computer Science and Engineering HCMUT

As we expand the range of problem-solving tasks

=> the representation becomes more complex

m

gGS

form

instance

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Frame

As we expand the range of problem-solving tasks, thesemantic-net representation becomes more complex

Minsky, 1975 A Framework for RepresentingKnowledge

Knowledge is encoded in packets, called frames

Slide 12Faculty of Computer Science and Engineering HCMUT

A Frame = A collection of attributes and associatedvalues (and possibly constraints on values)

Frame system = collection of frames that are connected

to each other

Attribute of one frame may be another frame

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Frame

Example

(defineInstance Tweety

(type Animals)(name "Tweety")

)

(defineTypeAnimals

(aliveT)(flies F)

)

Slide 13Faculty of Computer Science and Engineering HCMUT

(defineType Birds(super-typeAnimals(legs 2)

(flies T))

(defineType Mammals(super-typeAnimals)(legs 4)

)

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Frame(defineType Penguins

(super-typeBirds(flies F)

)

(defineType Cats

(defineInstance Opus(type Penguins(name "Opus")

(friend Bill))

(defineInstance Bill

Slide 14Faculty of Computer Science and Engineering HCMUT

-)

(defineType Bats

(super-typeMammals)(legs 2)(flies T)

)

(name "Bill")(friend Opus)

)

(defineInstance Pat(type Bats(name "Pat")

)

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FrameAnimals

Alive

Flies

T

F

Birds

Legs

Flies

2

T

Mammals

Legs 4

isa

Slide 15Faculty of Computer Science and Engineering HCMUT

Penguins

Flies F

Cats Bats

Legs

Flies

2

T

Opus

Name

Friend

Opus

Bill

Name

Friend

Bill

Pat

Name Pat

instance

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Frame

(defineInstance Opus(type Penguins(name "Opus")

(friend Bill))

(defineType Animals(alive T)(flies F)

)

Slide 16Faculty of Computer Science and Engineering HCMUT

type pus, engu nsname(Opus, Opus)

friend(Opus, Bill)

Rel(Animals, flies, F)

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FrameAnimals

Alive

Flies

T

F

Birds

Legs

Flies

2

T

Mammals

Legs 4

isa

Multipleinheritance

Slide 17Faculty of Computer Science and Engineering HCMUT

Penguins

Flies F

Cats Bats

Legs

Flies

2

T

Opus

Name

Friend

Opus

Bill

Name

Friend

Bill

Pat

Name Pat

instance

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Frame

Need an algorithm for traversing the isa hierarchy thatguarantees that specific knowledge will alwaysdominate more general facts.

Need an inheritance algorithm that reports theambiguity.

Slide 18Faculty of Computer Science and Engineering HCMUT