Lecture 7: 17/5/1435

knowledge Representation

Lecturer/ Kawther Abask.albasheir@sau.edu.sa

363CS – Artificial Intelligence

Introduction Real knowledge representation and reasoning

systems come in several major varieties. These differ in their intended use, expressivity,

features,… Some major families are

1. Logic programming languages

2. Theorem provers

3. Rule-based or production systems

4. Semantic networks

5. Frame-based representation languages

6. Databases (deductive, relational, object-oriented, etc.)

7. Constraint reasoning systems

8. Description logics

9. Bayesian networks

10. Evidential reasoning

What is Knowledge?

data – primitive verifiable facts, of any representation. Data reflects current world,often voluminous frequently changing.

information – interpreted dataknowledge – relation among sets of data

(information), that is very often used for further information deduction. Knowledge is (unlike data) general. Knowledge contains information about behaviour of abstract models of the world.

Data, Information, Data, Information, KnowledgeKnowledge? ?

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DATA

INFORMATION

KNOWLEDGE

WISDOM

Non-algorithmic(heuristic)

Algorithmic

Non-programmable

programmable

Knowledge Knowledge Representation Representation TechniquesTechniques

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TECHNIQUES

Object-Attribute Value

Frames

Semantic Networks

Logic

Rules

Object-Attribute-Value Object-Attribute-Value (OAV)(OAV)

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Using fact : “

•Eg: The ball’s color is red (assign red to the ball’s color) The object can be physical (eg: car, books) or abstract (eg: love, hobby).

•The value can be numerical, string or Boolean! It could be either single or multi valued from different attributes and objects.

Used in MYCIN

OAV Triplets Diagram OAV Triplets Diagram (i)(i)

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Fact :=: “The chair’s color is red and priced at $ 35.00 ”

CHAIR

RED

$ 35.00

Color

Priced

Object Attribute Value

OAV Triplets Diagram OAV Triplets Diagram (ii)(ii)

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Fact :=: “TIN 313 is a compulsory subject for MSc Int Sys., code for Artificial Intelligence, and taught by Mr Yousef Salahat”

TIN 313

MSc Int. Sys

Mr Yousef Salahat

Compulsory subject

Taught

Artificial Intelligence

Code

Rules BasedRules Based

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IF condition THEN action statements.      (premise              (goal      antecedent)          consequent)

•Example IF “Temperature is hot” THEN “turn on the air-conditioning system”

Rules Based System (I)Rules Based System (I)

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Rule 1:IF the ball’s color is red THEN I like the ball.

Rule 2:IF I like the ball THEN I will buy the ball.

IF ball’s color = red THEN like = ball

IF like = ball THEN will buy the ball

Ball’s color = red

Like = ball

Will buy = ball

Question: Ball’s color?

Answer: Red1

2

3

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Working Memory

Knowledge Base

Rules Based System (II)Rules Based System (II)

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•Rule 1: IF x has a sore throat AND suspect bacterial infectionTHEN x has strep throat

•Rule 2:IF x temperature is > 37 cTHEN x has a fever

•Rule 3:IF x has been sick > a monthAND x has a feverTHEN suspect bacterial infection

•Patient’s temperature = 38 c

•Patient has been sick > 2 months

•Patient has a sore throat

•Conclusion ?

Patient has Strep throat

38حرارة المريض

المريض تعبان من شهرين

المريض لديه التهاب حلق

المريض لديه بكتيريا في الحلق

The Example of Semantic The Example of Semantic Networks (Bird)Networks (Bird)

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FACT : Parrot is a bird. Typically bird has wings and travel by flying. Bird category falls under animal kingdom. All animal requires air to breathe. Ostrich is a bird but travels by walk.

AnimalAnimalBirdBird

WingsWings

ParrotParrot AirAir

OstrichOstrich

WalkWalk

FlyFly

is-a

travel

travel

has

is-a

Breathe

“exceptional handling”

Frames StructureFrames Structure

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Frame Name: BIRD

Properties:

Color = unknown

Wings = 2

Flies = True

Frame Name: OSTRICH

Properties:

Color = brown/dark

Wings = 2

Flies = False

Class Name: BIRD

LogicLogic المنطق الرياضي المنطق الرياضي

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•The oldest representation existed

•Implemented using PROLOG, LISP programming language.

Logical OperatorsLogical Operators

General Name

Formal Name

Symbols

Not Negation

And Conjunction

Or Disjunction

If… Then/Implies

Conditional

If and only if Biconditional

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FactsFacts

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•Artificial intelligence is a computer system

•Cat is an animal

Or combine

•Ahmed mother is married to Khalid father = True

•Cat is human = false

RulesRules القواعدالقواعد

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•Easy come easy go

•every way has an answer

or

If

• animal give milk it is a mammal

Predicate Calculus Logic Predicate Calculus Logic (FOPL)(FOPL)

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operator (variables_1, variables_2,…)

EXAMPLES:

COMPUTER_COURSE(ARTIFICIAL_INTELLEGIENCE)

ANIMAL(CAT)

Mathmatical LogicMathmatical Logic

Meaning Symbol

For All

Exist

NOT

And

OR v

Then

Greater than gt

Less than lt

Greater than or equal ge

Less than or equal le

equal =

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Predicate Calculus Logic Predicate Calculus Logic (FOPL)(FOPL)

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•Example: “She likes chocolate” likes (she, chocolate).

•Universal quantifier (X) to show all object is true [Eg: All students (X (student (X))]

• Existential quantifier (X) to show existence / partial object is true [ Eg: Some people ( X (people (X))]

The Example of FOPLThe Example of FOPL

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Normal: “If it doesn’t rain today, Ahmad will go to the beach. FOPL: rain( today) go(Ahmad, beach)

Normal: “All volleyball players are tall” FOPL: X (volleyball_player (X) tall (X))

Normal: Some people like durian. FOPL: X (person(X) likes(X, durian))

Normal: Nobody likes wars FOPL: X likes (X, wars)

Implementing Propositional Implementing Propositional LogicLogic

P Q P Q

T T T

T F F

F T T

F F T

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“IF the battery is dead THEN the car won’t start”

•P = battery is dead & Q = car won’t start

•Battery is dead = T, car won’t start = T

•“Battery not dead” = F, “car will start” = F

•Equivalence to P Q

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Mammals Mammals

PersonPerson

Female Person

Female Person

Male

Person Male

Person

Mariam Mariam Ahmad Ahmad

HasMother

Sister of

Subset of

Member of

Subset-of

Subset-of

Member of

2legs

legs

1

Example:

Sister_of(Mariam,Ahmed)Legs(Ahmed)=1Member_of(Mariam,Female_Person)

Ahmed frame: : Ahmed

Member of : Male PersonLegs: 1

Has Sister : Mariam

Person frame:Person:

Subset of : MammalLegs: 2

Has Mother : Female Person

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Example

:حالة استثنائيةأحمد له رجال

واحدة بينما لكل البشر رجالن

ResolutionTheorem. Resolution is sound. Thai

is, all derived formulas are entailed by the given ones

Theorem: Resolution is refutationally complete.

That is, if a clause set is unsatisfiable, then Resolution will derive the empty clause eventually.

If a clause set is unsatisfiable and closed under the application of resolution inference rule then it contains the empty clause.

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