Post on 21-Feb-2018
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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