1. Pertemuan 5 Knowledge Representation Issues
Matakuliah : T0264/Inteligensia Semu
Tahun : Juli 2006
Versi : 2/1
Pertemuan 5 Knowledge Representation Issues

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Learning Outcomes
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3. Outline Materi
Materi 1
Materi 2
Materi 3
Materi 4
Materi 5

4. 4.1 Representations and Mappings
Mapping between Facts and Representation

5. 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.

6. Simple Example “Spot is dog” dog(Spot) x : dog(x)  hastail(x)
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

7. 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 ?

8. Three Representation of a Mutilated Checkerboard

9. Representation of Facts

10. 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.
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.
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.
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.

11. 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.

12. Inheritable Knowledge
Attribute Isa used to show class inclusion.
Attribute Instance used to show class membership.

13. Viewing a Node as a Frame
Baseball-Player
Isa : Adult-Male
bats :(EQUAL handed)
height : 6-1
batting-average : .252

14. Algorithm : property Inheritance
To retrieve a value V for attribute A of an instance object O:
Find O in the knowledge base.
If there is a value there for the attribute A, report that value.
Otherwise, see if there is a value for the attribute instance. If not, then fail.
Otherwise, move to the node corresponding to that value and lock for a value for the attribute A. If one is found, report it.
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.

15. 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 :
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 ?

16. There two attributes that are of very general significance :
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

17. 4.3.2. Relationships among Attributes
Terdapat 4 sifat yang perlu diketahui :
Inverses
Existence in an isa hierarchy
Techniques for reasoning about value
Single-value attributes

18. 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,...

19. 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.

20. 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

21. 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

22. 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))

23. 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)))

24. 4.3.4 Representing Sets of Objects
There are two ways to state a definition of a set and its element :
To list the members : Such a specification is called an extensional definition
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) }

25. 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

26. Represent efficiently sequences of problem states A Similarity Net
4.4 The Frame Problem
Represent efficiently sequences of problem states
A Similarity Net
CHAIR
TABLE
STOOL
DESK
SIDEBOARD
too big, no back
BENCH
no back,too wide
too high, no back
no knee room
drawers

27. << CLOSING>>
End of Pertemuan 5
Good Luck