Matakuliah
Tahun
Versi
: T0264/Inteligensia Semu
: Juli 2006
: 2/1
Pertemuan 5
Knowledge Representation Issues
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Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• << TIK-99 >>
• << TIK-99>>
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Outline Materi
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Materi 1
Materi 2
Materi 3
Materi 4
Materi 5
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4.1 Representations and Mappings
Mapping between Facts and Representation
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Representations and Mappings
 Two different kinds of entities :
- Fact : truths in some relevant world. These the thing we
want to represent.
- Representations of facts in some chosen formalism.
These are the things we will actually be able to
manipulated.
 One way to think of structuring these entities is as two
level :
+ The knowledge level, at which facts are described.
+ The symbol level, at which representations of objects at
the knowledge level are defined in terms of symbols that
can manipulated by programs.
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Simple Example
Consider the English sentence :
“Spot is dog”
Fact representations :
dog(Spot)
Logical representation of the fact :
x : dog(x)  hastail(x)
Using deductive mechanism of logic :
hastail(Spot)
New representation using backward mapping :
Spot has a tail
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The Mutilated Checkerboard problem
• Consider a normal checker board from
which two squares, in opposite corners,
have been removed. The task is to cover
all the remaining squares exactly with
dominoes, each of which covers two
squares. No overlapping, either of
dominoes on to of each other or of
dominoes aver boundary of the mutilated
board are allowed.
Can this task be done ?
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Three Representation of a Mutilated Checkerboard
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Representation of Facts
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4.2 Approaches to Knowledge Representation
Properties of a Representation System
• Representation adequacy : the ability to represent all of
the kinds of knowledge that are needed in the domain.
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Inferential adequacy : the ability to manipulate the
representational structures in such a way as to derive new
structures corresponding to new knowledge inferred from old.
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Inferential efficiency : the ability to incorporated into the
knowledge structure additional information that can be used to
focus the attention of the inference mechanism in the most
promising directions.
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Acquisitional efficiency : the ability to acquire new
information easily. The simplest case involves direct insertion, by
person, of new knowledge into data base. Ideally, the program
itself would be able to control knowledge acquisition.
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Inheritable Knowledge
• In order to support property inheritance, object
must be organized into classes and classes
must be arranged in a generalization hierarchy.
• Some additional baseball knowledge inserted
into a structure that is so arranged.
• Line represent attributes, boxed nodes represent
object and values of attributes of object.
• The structure shown in figure is a slot and filler
structure. It may also called a semantic network
or a collection of frames.
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Inheritable Knowledge
Attribute Isa used to show
class inclusion.
Attribute Instance used to
show class membership.
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Viewing a Node as a Frame
Baseball-Player
Isa
bats
height
batting-average
: Adult-Male
:(EQUAL handed)
: 6-1
: .252
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Algorithm : property Inheritance
To retrieve a value V for attribute A of an instance object O:
1. Find O in the knowledge base.
2. If there is a value there for the attribute A, report that
value.
3. Otherwise, see if there is a value for the attribute
instance. If not, then fail.
4. Otherwise, move to the node corresponding to that
value and lock for a value for the attribute A. If one is
found, report it.
5. Otherwise, do until there is no value for the isa
attribute or until an answer is found :
a. Get the value of the isa attribute and move to that node.
b. See if there is a value for the attribute A. If there is, report it.
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4.3 Issues in Knowledge Representation
Before embarking on a discussion of specific mechanisms
that have been used to represent various kind of real-world
knowledge, several issues that cut across all of them :
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Are there any basic attributes of objects ?
Are there any basic relationship among objects ?
At what level should knowledge be represented ?
How should sets be representation ?
How should knowledge be accessed ?
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4.3.1 Important Attributes
There two attributes that are of very general
significance :
•Attribute Instance to show class membership
Jadi atribut instance adalah atribut dengan argumen pertama
berupa obyek dan argumen kedua berupa klas dari obyek
tersebut
•Attribute Isa to show class inclusion or class
relationship
Jadi atribut Isa adalah subuah atribut yang menunjukan
hubungan antar sub klas
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4.3.2. Relationships among Attributes
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1.
2.
3.
4.
Terdapat 4 sifat yang perlu diketahui :
Inverses
Existence in an isa hierarchy
Techniques for reasoning about value
Single-value attributes
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Representing Inverses
• Reversible representations that ignore focus :
Team(Pee-Wee- Reese, Brooklyn-Dodgers)
• Pairs of focused entities :
- one associated with Pee Wee Reese :
team = Brooklyn-Dodgers
- one associated with Brooklyn Dodgers :
team-members = Pee-Wee-Reese,...
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An isa hierarchy of attributes
• Just as there are classes of objects
specialized subsets of those classes, there
are attributes and specializations of
attributes.
• In tne case of attributes, they support
inheriting information about such thing as
constraints on the values that the attribute
can have and mechanisms for computing
those value.
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Techniques for reasoning about value
• Information about the type of the value
• Constraints on the value, oftenstated in
terms of related entities
• Rules for computing the value when is
needed
• Rules that describe actions that should be
taken if a value ever become known
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Single-value attributes
Several different approaches to providing
support for single-valued attributes :
• Introduce an explicit notation for temporal
interval
• Assume that the only temporal interval that
is of interest is now
• Provide no explicit support
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4.3.3 Choosing the Granularity of Representation
Suppose we are interested in the following fact :
John spotted Sue.
We could represent this as
spotted(agent(John),object(Sue))
Questions :
Who spotted Sue ?
Did John see Sue ?
We could add facts, e.g.:
spotted(x,y)  saw(x,y)
An alternative representation :
saw(agent(John),object(Sue),timespan(briefly))
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Are There Primitive Concepts ?
Marry is Sue ‘s cousin.
• Marry = daughter(brother(mother(Sue)))
• Marry = daughter(sister(mother(Sue)))
• Marry = daughter(brother(father(Sue)))
• Marry = daughter(sister(father(Sue)))
An alternative :
• Marry = child(sibling(parent(Sue)))
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4.3.4 Representing Sets of Objects
There are two ways to state a definition of a set and its element :
1. To list the members : Such a specification is called an
extensional definition
2. To provide a rule that : Such a rule is called an instentional
definition
Intensional and Extensional Representation
Extensional :
{Earth}
Intensional :
{x : sun-planet(x)  human-inhabited(x)}
{x : sun-planet(x)  nth-farthest-from-sun(x,3)}
{x : sun-planet(x)  nth-biggest(x,5) }
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4.3.5 Finding the Right Structures as Needed
Selecting an Initial Structure
• Index structures by English words
- John flew to New York.
He rode in a plane from one place to another.
- John flew a kite.
* He held a kite that was up in the air.
- John flew down the street.
* He moved very rapidly.
- John flew into a rage.
An idiom
• Index structures by concepts
• Use one major clue
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4.4 The Frame Problem
Represent efficiently sequences of problem states
BENCH
A Similarity Net
CHAIR
no back,too wide
too high, no back
too big, no back
TABLE
STOOL
drawers
DESK
SIDEBOARD
no knee room
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<< CLOSING>>
End of Pertemuan 5
Good Luck
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