semantic nets

5/17/2018 Semantic Nets - slidepdf.com

http://slidepdf.com/reader/full/semantic-nets 1/39

All rights reserved © L. Manevitz Lecture 7 1

Artificial IntelligenceRepresenting Commonsense

Knowledge

L. Manevitz




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.




Semantic Network Approach

• Nodes and Slots:

Nodes are objects,

or classes,or properties.

Slots are of different types.




A Semantic Network

Mammal

Person Nose

Pee-Wee-ReeseBlue Brooklyn-Dodgers

Is-a

has-part

instanceteam

uniform-

color




Representing Nonbinary

Predicates• Unary Predicates can be rewritten as

binary ones.

man( Marcus)

could be rewritten as

instance(Marcus,Man)




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




A Semantic Net Representing

a Sentence

“John gave the book to Mary.”

Give

EV7 BK23

Mary

Johnobject

beneficiary

agent

instance

Book

instance




Some Important Distinctions

First try:

Second try:

John 72height

John

H1

height

Bill

H2

height

greater-than




Some Important Distinctions

cont.

Third try:

72

value

John

H1

height

Bill

H2

height

greater-than




Partitioned Semantic Nets

Bite

b m

Dogs

d

Is-a

victimassailant

Mail-carrier

Is-aIs-a

a) The dog bit the mail carrier.




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





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





d) Every dog has bitten every mail carrier.

Bite

b md

Is-a

victimassailant

Mail-carrier

Is-aIs-a

gGSIs-a

form

DogsSA

S1




Inheritance

• Is-a slot – appears between objects and

classes.

• ako slot – appears between subsets.




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.




Inheritance - Example

Is-a

shape

ako

Block

Brick

Brick12

rectangular

Is-a

ako

Wedge

Wedge18

shapeTriangular




If-needed Inheritance -Procedure



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.





If-needed Inheritance - Example

Weight (if-needed)

Block

Brick

Brick12

Block-weight-

procedure

400

11

Volume

Density




Example cont.

Weight

Block

Brick

Brick12 400

11

Volume

Density

4400

Weight is activated

by request for the

weight of Brick12 !




Default Inheritance Procedure



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.





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 !




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




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.




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.




Frames

• Frames : A collection of nodes that

describe a stereotyped object, act or event.

• Example : newspaper report.




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




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.





Earthquake13

place Lower Slabovia

Today

25

500,000,000

8.5

day

fatalities

damage

magnitude

fault Sadie Hawkins




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 .




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.





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.





• 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.




Scripts




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




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)





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





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)





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)





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)

semantic nets

Documents