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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
Object Attribute Value
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
Object Attribute Value
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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)