semantic nets
TRANSCRIPT
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All rights reserved © L. Manevitz Lecture 7 1
Artificial IntelligenceRepresenting Commonsense
Knowledge
L. Manevitz
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Definitions
• Representation – a set of syntactic and semantic
conventions that make it possible to describe
things.
• Syntax – specifies the symbols that may be used
and the ways those symbols may be arranged.
• Semantics – specifies how meaning is embodied
in the symbol arrangements allowed by thesyntax.
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Semantic Network Approach
• Nodes and Slots:
Nodes are objects,
or classes,or properties.
Slots are of different types.
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A Semantic Network
Mammal
Person Nose
Pee-Wee-ReeseBlue Brooklyn-Dodgers
Is-a
has-part
instanceteam
uniform-
color
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Representing Nonbinary
Predicates• Unary Predicates can be rewritten as
binary ones.
man( Marcus)
could be rewritten as
instance(Marcus,Man)
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Representing Nonbinary
Predicates cont.• N-Place Predicates
score(Cubs,Dodgers,5-3)
becomes Game
G23 5-3
Dodgers
Cubs
Is-a
score
home-team
visiting-
team
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A Semantic Net Representing
a Sentence
“John gave the book to Mary.”
Give
EV7 BK23
Mary
Johnobject
beneficiary
agent
instance
Book
instance
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Some Important Distinctions
First try:
Second try:
John 72height
John
H1
height
Bill
H2
height
greater-than
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Some Important Distinctions
cont.
Third try:
72
value
John
H1
height
Bill
H2
height
greater-than
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Partitioned Semantic Nets
Bite
b m
Dogs
d
Is-a
victimassailant
Mail-carrier
Is-aIs-a
a) The dog bit the mail carrier.
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Partitioned Semantic Nets cont.
b) Every dog has bitten a mail carrier.
Bite
b m
Dogs
d
Is-a
victimassailant
Mail-carrier
Is-aIs-a
g
GS
Is-aform
SA
S1
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Partitioned Semantic Nets cont.
c) Every dog in town has bitten the
constable.
Bite
b c
Town-Dogs
d
Is-avictimassailant
Constables
Is-aIs-a
g
GS
Is-aform
DogsSA
S1
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Partitioned Semantic Nets cont.
d) Every dog has bitten every mail carrier.
Bite
b md
Is-a
victimassailant
Mail-carrier
Is-aIs-a
gGSIs-a
form
DogsSA
S1
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Inheritance
• Is-a slot – appears between objects and
classes.
• ako slot – appears between subsets.
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Inheritance -Procedure
F the given node; S the given slot;
1. Form a Queue of F and all class nodes connected to Fvia Is-A node. F is at top of Queue.
2. Until Queue is empty or default has been found
determine if the first element of Queue has a value inits S slot:
a. Yes – a value has been found.
b. No – remove the first element from Queue and add the nodesrelated to the first element by AKO slots to the end of Queue.
3. If a value has been found say that this is the defaultvalue of F‟s S slot.
Otherwise announce Failure.
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Inheritance - Example
Is-a
shape
ako
Block
Brick
Brick12
rectangular
Is-a
ako
Wedge
Wedge18
shapeTriangular
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If-needed Inheritance -Procedure
F the given node; S the given slot;
1. Form a Queue of F and all class nodes connected to Fvia Is-A node. F is at top of Queue.
2. Until Queue is empty or successful if-needed procedure
has been found determine if the first element of Queuehas a procedure in the If-Needed facet of its S slot:
a. Yes – if the procedure produces a value than a value has beenfound.
b. No – remove the first element from Queue and add the nodes
related to the first element by AKO slots to the end of Queue.3. If a value has been found say that the value found is the
value of F‟s S slot.
Otherwise announce Failure.
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If-needed Inheritance - Example
Weight (if-needed)
Block
Brick
Brick12
Block-weight-
procedure
400
11
Volume
Density
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Example cont.
Weight
Block
Brick
Brick12 400
11
Volume
Density
4400
Weight is activated
by request for the
weight of Brick12 !
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Default Inheritance Procedure
F the given node; S the given slot;
1. Form a Queue of F and all class nodes connected to Fvia Is-A node. F is at top of Queue.
2. Until Queue is empty or default has been found
determine if the first element of Queue has a value inthe Default facet of its S slot:
a. Yes – if the first element has a value than a value has beenfound.
b. No – remove the first element from Queue and add the nodes
related to the first element by AKO slots to the end of Queue.3. If a value has been found say that the value found is the
default value of F‟s S slot.
Otherwise announce Failure.
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Default Inheritance - Example
Is-a
Color (Default)
ako
Block
Brick
Brick12
Red
Is-a
ako
Wedge
Wedge18
Color (Default)Blue
Has no default
color therefore
probably Blue
because of
Block‟s default
color !
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Perspective -Example
Is-a
Purpose
Support
Brick Structure
Is-a
Play Commemorate
Toy
shape
rectangular
Gift
perspectiveToy perspectiveStructure
perspectiveBrick12
Purpose
Is-a
Gift
Purpose
Is-a
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Special Links - Summary
• IS-A and AKO links make class
membership and subclass-class relations
explicit, facilitating the movement of knowledge from one level to another.
• VALUE facets make values explicit.
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Special Links – Summary cont.
• IF-NEEDED facets make procedures purposes
explicit, and they relate procedures to the classes
those procedures are relevant to.
• DEFAULT facets make likely values explicit
without implying certainty.
• Perspectives make context sensitivity explicit,
preventing confusion and ambiguity.
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Frames
• Frames : A collection of nodes that
describe a stereotyped object, act or event.
• Example : newspaper report.
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Earthquake ExampleDisaster-event
Earthquake
Flood
Hurricane
EventKilled
Injured
Homeless
Damage
Magnitude
Fault
Crest
River
Wind-speed
Name
Place
Day
Time
Social-event
Birthday-party
Number-of-
guests
Host
Age
Birthday-
person
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Earthquake Example cont.
Earthquake Hits Lower Slabovia
• Today an extremely serious earthquake of
magnitude 8.5 hit Lower Slabovia killing25 people and causing $500,000,000 in
damage. The president of Lower Slabovia
said the hard-hit area near the Sadie
Hawkins fault has been a danger zone for
years.
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Earthquake Example cont.
Earthquake13
place Lower Slabovia
Today
25
500,000,000
8.5
day
fatalities
damage
magnitude
fault Sadie Hawkins
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Earthquake Summary Pattern
• An earthquake occurred in value in
location slot value in day slot . There were
value in fatalities slot fatalities and value
in damage slot in property damage. The
magnitude was value in magnitude slot on
the Richter scale, and the fault involved
was the value in fault slot .
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Instantiated Earthquake
Summary Pattern
• An earthquake occurred in Lower Slabovia
today . There were 25 fatalities and $500
million in property damage. The magnitude
was 8.5 on the Richter scale, and the fault
involved was the Sadie Hawkins.
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Earthquake Example cont.
Earthquake Study Stopped
Today, the President of Lower Slabovia killed 25
proposals totaling $500 million for research in
earthquake prediction. Our Lower Slaboviancorrespondent calculates that 8.5 research
proposals are rejected for every one approved.
There are rumors that the President‟s science
advisor, Sadie Hawkins, is at fault.
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Earthquake Example cont.
• The Earthquake Study Stopped story
could be summarized, naively, as though it
were the story about an actual earthquake,
producing the same frame as the
Earthquake Hits Lower Slabovia story
does.
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Scripts
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Scripts
• Example - Restaurant script.
Script: Restaurant Roles: S=Customer
Track: Coffee Shop W=Waiter
Props: Tables C=Cook
Menu M=Cashier
F=Food O=Owner
Check
Money
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Restaurant Example cont.
Entry conditions : S is hungry
S has money
Results : S has less money
O has more money
S is not hungry
S is pleased (optional)
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Restaurant Example cont.
Scene 1: Entering
S PTRANS S into restaurantS ATTEND eyes to tables
S MBUILD where to sit
S PTRANS S to table
S MOVE S to sitting position
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Restaurant Example cont.
Scene 2: Ordering(menu on table) (W brings menu) (S asks for menu)
S PTRANS menu to S S MTRANS signal to W
S MTRANS „need menu‟ to W W PTRANS W to table
W PTRANS W to menu
W PTRANS W to tableW ATRANS menu to S
S MTRANS W to table*S MBUILD choice of FS MTRANS signal to WW PTRANS W to tableS MTRANS „I want F‟ to W
W PTRANS W to C
W MTRANS (ATRANS) to C
C DO (prepare F script) to
Scene 3
C MTRANS „no F‟ to W W PTRANS W to SW MTRANS „no F‟ to S
(go back to *) or
(go to Scene 4 at no pay
path)
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Restaurant Example cont.
Scene 3 : Eating
C ATRANS F to W
W ATRANS F to SS INGEST F
(Option : Return to Scene 2 to order more;
otherwise go to Scene 4)
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Restaurant Example cont.
Scene 4 : Exiting
S MTRANS to W
W PTRANS W to S
W MOVE (write check) (W ATRANS check to S)
W ATRANS check to S
S ATRANS tip to W
S PTRANS S to M
S ATRANS money to MS PTRANS S to out of restaurant
(No pay path)