Chp02 KR Complete

8/7/2019 Chp02 KR Complete

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KNOWLEDGE

REPRESENTATION

1


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Knowledge,

like love,is one of those words that

everyone knows the meaning

of, yet finds hard to define.

Like love, knowledge has

many meanings.

Giarratano and Riley (1998)


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Intelligence requires knowledgeIntelligence refers to the capacity to

acquire and apply knowledge.


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Knowledge is an understanding which is gained

through

experience; familiarity with the way to do something to

perform a task;

an accumulation of facts, procedural rules or

heuristics.


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Knowledge can have many meanings. It is not justthe body of facts and principles accumulated by

human-kind or the act, or state of knowing, but alsothe familiarity with languages, concepts,procedures, rules, ideas, abstractions, places,customs, facts and associations as well as

information(Patterson, 1990)


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Facts

Procedural

Rules

HeuristicKNOWLEDGE


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Facts

A statement that relates a certain element of

truth about a subject matter or a domain Example:

milk is white

the sun rises in the East

and sets in the West


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Procedural rules

A rule that describes a sequence of relations

relative to the domain Example:

If the gas gauge shows

quarter-full or less,

then look for a gasoline

station


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Heuristic

Is a rule of thumb based on years of experience.

Example: If a person drives no more

than 5 miles above the

speed limit, then that

person is not likely to be

stopped for speeding.


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Priori

Knowledge which cannot be denied

Considered to be universally true

Logic statements, mathematical laws

e.g. everybody will die, ice is cold

Posteriori

Knowledge derived from the senses, which can be true or false.

The truth can be denied by sensory experience or on the basis of newknowledge


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Tacit

Unconscious knowledge that cannot be expressed by language spontaneous actions without any significant amount of effort

Eyes blinking, breathing

Explicit

Documented knowledge


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Basic Types of

Knowledge

Procedural(how to do)

Structural

(mental model)

Meta

Knowledge(about other)

Heuristic

(shortcut)

Declarative

(what it is)


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Procedural

Knowledge on the process of doing something

It provides direction on how to do something via rules, strategies,

agendas as well as procedures

Declarative

A passive knowledge expressed as statements of facts about theworld


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Meta-knowledge

Knowledge about knowledge

Knowledge on knowing which knowledge to use to solve a problem Always used by experts to enhance the efficiency of problem solving

Heuristic

Knowledge which is gained through experience and translated into

instinct or intuition

Often displayed individual expertise


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Procedural knowledge to boil an egg we must do then

Declarative knowledge

my room no. is 2103

Meta-knowledge if you want to know about heart attack, please read this book

Heuristic knowledge the clouds looks dark and heavy, heavy rain might fall

Structural Knowledge a cat has four legs


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Data

Information

+ CT

Knowledge

This is

CTsphone

no.!


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Meta

Knowledge

Knowledge

Information

Data

Noise


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DocumentedExp:printed &

electronic media

Not documented

Exp: experience


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Knowledge representation is

a science of translating

actual knowledge intoa format that can be

used by the computer.


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Knowledge Source

Knowledge

Representation

Knowledge Usage


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Why needs to represent knowledge?...

You are given a projectto develop a systemthat can diagnoseheart attack?

How can you get information about heart attack?

How do you understand the knowledge?

Which knowledge to get into computer?


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KnowledgeRepresentation

Methods Logic

ject

Rule


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OAV ObjectAttributeValue

Color Gold

Object Attribute Value


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Using fact : form of declarative knowledge


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Refer to particular properties value of object Eg: The balls color is red (assign red to the balls

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 fromdifferent attributes and objects.


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Colour Gold


Car Colour

Gol

d


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Fact :=: The chairs color is red and priced at RM35.00

CHAIR

RED

RM 35.00

Color

Price



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Fact :=: I have a brother named Johnny. The 8years-old brother likes to play tennis and football.

johnny

male

8 years old

gender

age

tennis

hobby

football


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Discussion Describe aboutDoraemon


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Semantic Network

Animals


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Definition method of knowledge representation using a graph made up

of nodes and arcs

Graphical view of problems important objects,properties and relationships.

Nodes represent objects & arcs represent therelationship.

Arcs are commonly labeled with terms IS-A orHAS


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FACT : Parrot is a bird. Typically bird has wings and travel by

flying. Bird category falls under animal kingdom. All animalrequires air to breathe. Ostrich is a bird but travels by walking.

AirAnimalBird

Wings

Parrot

Ostrich

Walk

Fly

is-a

trave

l

trave

l

has

is-a

breathe


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Mammals

Human

Female

Male

Two legs

Mariam

AhmadSystem

Analyst

Wheel

chair

Degree

BIT(Hons)

Walkis-a

has

mother-of

has

is-a

is-ais-a

is-a

travel-by

travel-by


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Frame

Definition :: a datastructure for representingstereotypical knowledge ofsome concept or object


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An extension version of semantic network calledschema (proposed by Barlett, 1932).

Basic concept of object oriented programming

(proposed byMinsky, 1975). Class frame general characteristics of some

common objects (Eg: class frame bird refer tocommon properties of bird).

Instance frame to describe unique characteristicfrom class frame (Eg: class ostrich from classframe bird)


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Example

Frame Name:

B

IRDProperties:

Color =

Wings = 2

Flies = True

Frame Name: OSTRICH

Properties:

Color =

brown/dark

Wings = 2

Flies = False

Class Name: BIRD


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Two l t

of fr

Slot

Is the characteristic

that describe an

object

Exp: color, food, no.of wings,

Facet

Value for slot

Exp: yellow, 1,

worm,


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Example

Frame Name:

BIRDProperties:

Color =

Wings = 2

Flies = True

Slot Facet


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Rule

Definition :: Rules a knowledge structure thatrelates some known information to other

information and that can be concluded or inferredto be known


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Is a form of procedural knowledge associates given information to some action.

Structure connects antecedents (premises)and consequents (conclusions).


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Statement IF antecedent and THEN consequent

IF THEN

IFthirsty THEN drink_a_water


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Example: Diagnosing strep throat (knowledge base)

Rule 1:

IF x has a sore throatAND suspect bacterial infectionTHEN patient 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


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Logic


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Oldest form of KR in computer Concerned with the truthfulness of a chain of

statements 2 kinds of logic:

Propositional Logic

Predicate Calculus

Implemented in PR

OLOG

(Programming inLogic) language


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E.g.it_is_raining

kitty_is_outside

kitty_gets_wet

Elementary propositions or atomic sentences cannot bebroken down into smaller meaningful units.

Often represented using symbols, e.g. P, Q,A etc.


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Manipulate basic Boolean logic operations (AND,OR, NOT, IMPLIES, EQUIVALENCE.)

E.g.:

Normal :Today is raining, therefore I will miss theclass

Logic : today_raining i_will_miss_class

Combining two or more PL forms compound propositions(CP) or formulae.

CP consists of propositions and logical operators.


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Logical operators:

General Name Formal Name Symbols

Not Negation

And Conjunction

Or DisjunctionIf Then/Implies Conditional

If and only if Biconditional

m

p


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Propositional Logic Example Example 1:

Normal:The sky is blue and windy. It is really great for picnic

Logic: sky_blue windy great_for_picnic

Example 2: Normal: If the weather is cloudy, then it will be raining. If it is

raining, people will stay at home.

Logic: (weather_cloudy raining) (raining people_stay_home).

Example 3: Normal: I will rather stay if and only if it is raining.

Logic: i_will_staym raining


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Propositional Logic Discussion

Question: Transform each of the following statements

into propositional logic:

a) Today is Tuesday and it is a very lovely day.

b) It rained yesterday, therefore I've missed my lecture.

c) All men are mortals.

d) Sintok is a district within Kedah


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Nested formulae important to express the actual meaning

of a wff. E.g:

it_is_raining kitty_is_outsidepkitty_gets_wet

(1) (it_is_raining kitty_is_outside) pkitty_gets_wet

(2) it_is_raining (kitty_is_outsidepkitty_gets_wet)


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Order of precedence

m

p

The above determines the principal operator to split aformulae into smaller units.

Purpose: to indicate the actual meaning of a formulae. E.g.:

P PpQpQ

A BCm P QpR


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Truth table a common method to prove the

truth value of any statement written in PL.

P Q P PQ PQ PpQ PmQ

T T F T T T T

T F F F T F F

F T T F T T F

F F T F F T T


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Truth table determines the category of formula Tautology formula is always T regardless of the truth

values of its propositions.

E.g. (P(PpQ))pQ Contingent formula is sometimes T and sometimes F,

depending on the truth values of its propositions E.g. (AB)pC

Inconsistent formula is always F regardless of the truth

values of its propositions E.g. P(P)


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Limitation Cannot express universality of objects

E.g.

all computers have processor; all birds fly.

Cannot express existence / inexistence / partial

quantity of objects E.g. there are some birds which cannot fly

none of us is immortal


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Also known as First Order Predicate Logic (FOPL).

This method overcomes the limitations of

propositional logic through use of quantifiers andvariables.

Main structure

argument (i.e. variables and/or constants) islinked by operator (i.e. functor).


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A predicatefunctor(argument1, argument2)

A predicate consists offunctor and zero or more arguments Functor (or predicate name) relates the arguments

Argument can be variables or constant

Variables

A symbol in capital letter or a word begins with uppercase letter

Represent general classes of objects or properties


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E.g.:

teach(X,Y)

X and Y can be substituted with any value/constantsuch as:

dave and comp5346,

resulting in:

teach(dave,comp5346)


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Constant

A symbol or string of letters begins with lower caseletter

Represent specific classes of objects or properties

E.g.:

dave and comp5436 are constants

dAVe and coMP5436 are also valid constants

What about Dave and COMP5436? Are they thevalid constants? Why?


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Basic ideafunctor(variable_1, variable_2, .) E.g.

she likes chocolatelikes(she, chocolate)

tweety is a bird

isa(tweety,bird) ORbird(tweety)


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Universal quantifier (X) means for all

Indicates the expression is T (i.e. true) forALL values of

designated variables E.g.:X likes(X,icecream)

For all values ofX, the statement X likes ice cream is true

E.g.: all birds fly is represented asX (bird(X) flies(X))

This also means no birds do not fly, thus it can also berepresented asXflies(X).


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Existential quantifier (X) means there exist.

Indicates the expression is T (i.e. true) forSOME values

of designated variables (at least one value exists thatmakes the statement T)

E.g.: some children like ice cream

Is represented as:

X likes(X,icecream) ORChildren likes(Children,icecream)

Can also be represented asX likes(X,icecream) .As thestatement also means not all children like ice cream.

E.g.: some birds do not fly is represented as X (bird(X) flies(X))


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E.g. 1: Normal: If it doesnt rain today,Ahmad will go to the beach

FOPL: rain(today) go(Ahmad, beach)

E.g. 2:

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

E.g. 3: Normal:Some people like durian.

FOPL: X (person(X) likes(X, durian))

E.g. 4: Normal: Nobody likes war

FOPL: X likes (X, war) OR X likes(X,war)

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