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Knowledge RepresentationRule-Based RepresentationFrame-Based RepresentationSemantic-Networks

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April 18, 2023 3

What is frame? A frame is a data structure with typical knowledge about a

particular object or concept. Followings are two typical frames with knowledge about airline

passengers. Both frames have the same structure. Each frame has its own name & a set of attributes or slots,

associated with it.

QUANTAS BOARDING PASSCarrier: QUANTAS AIRWAYSName: MR N BLACKFlight: QF 612Data: 29DECSeat: 23AFrom: HOBARTTO: MELBOURNEBoarding:0620Gate: 2

AIR NEW ZEALAND BOARDING PASSCarrier: AIR NEW ZEALANDName: MRS J WHITEFlight: NZ 0198Data: 23NOVSeat: 27KFrom: MELBOURNETO: CHRISTCHURCHBoarding:1815Gate: 4

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Frames as knowledge representation technique

The concept of a frame is defined by a collection of slots or attributes.

Each slot describes a particular attribute or operation of the frame.

Slots are used to store values.A slot may contain a default value or a pointer to

another frame, a set of rules or procedure by which the slot value is obtained.

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There are 3 types of relationships between objects:Generalization:

It denotes “a-kind-of” or “is-a” relationship between super-class and its sub-class.

For example, a car is-a vehicle, or in other words, Car represents a subclass of the more general super-class Vehicle.

Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation

How are objects related in a frame-based system?

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CLASS: Vehicle

CLASS: Boat CLASS: CarCLASS: Airplane

is-a is-a is-a

Superclass: Vehicle

Superclass: Vehicle

Superclass: Vehicle

Generalization


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Aggregation:It is “a-part-of” or “part-whole” relationship in

which several subclass representing components are associated with a super-class representing components are associated with a super-class representing a whole.

For example, an engine is a part of a car.



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CLASS: Car

CLASS:Chassis CLASS:Engine CLASS:Transmission

a-part-of

Superclass: Car Superclass:Car Superclass:Car

Aggregation

a-part-of a-part-of


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Association:It describes some semantic relationship

between different classes which are unrelated otherwise.

For example, Mr. Black owns a car.



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CLASS: Mr. Black

CLASS:House CLASS: Car CLASS: Computer

Superclass: Mr. Black

Superclass: Mr. Black

Superclass:Mr. Black

Association

Belongs-toBelongs-to

Belongs-to

ownsowns owns


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We can define the given problem in abstract way.Frames provide a way for the structured and

concise representation of knowledge. In a single entity, a frame combines all necessary

knowledge about a particular object or concept.During a search for a specific item, we go directly

to the item’s instance frame that contains the desired goal.


Advantages

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Idea behind the frame based system is easy, but implementation is difficult.

It can not distinguish between essential properties and accidental properties of a frame.

Hence, in a complex case, it is difficult to predict how these features will interact, or to explain unexpected interactions, which makes debugging and updating difficult.


Disadvantages

Semantic NetworkSN was first proposed by Quillian in 1966, as a model of

human memorySemantic network (SN) is a graph-based representationIt is a directed graphA SN is a network of nodes and links to represent the

definition of a concept (or a collection of concepts)The nodes represent conceptsThe links represent the relations between concepts

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Semantic NetworkIn these networks, objects are shown by nodes,

and links between the nodes describethe relationship between two objects, for

example,Mary is an instance of trainer, and trainer is a

type of consultant. A trainer trains a programmer and a

programmer is an employee.Joe is an instance of programmer.

From this we can clearly see the relationship that may exist between Mary and Joe.

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ExampleDraw a diagram representing the relationships between

Mary and Joe, indicating the relationship between a trainer, consultant, programmer and employee.

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ExampleSuch a diagram is the beginning of a semantic

network but this can be improved by more closely defining the nature of the relationships.

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InheritanceInheritance is concerned with how one object inherits

the properties of another object.

In the diagram you created in the previous activities,

identify from which classes Mary and Joe inherit

properties.

You should have been able to recognize that Mary, in

being a trainer, inherits the properties of the consultant

class and that Joe, in being a programmer, inherits the

properties of the employee class.April 18, 2023 17

Inheritance

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InheritanceYou should have been able to recognize that from this semantic

network it would be possible to conclude that the grass snake

Slither is a vegetarian and Slither eats meat. Clearly, these

conclusions are contradictory. Which conclusion we reach

depends where in the network we start and which links we

follow. This process is unreliable.

Thus, to perform inference using a semantic network you must

understand the meaning of the links and follow the correct links.

As the links can be many, and varied, performing inference

using a semantic network is complex and unreliable.

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April 18, 2023 20

Vertebrata Cat Fur

Animal Mammal Bear

FishWater

Whale

is-an is-a

is-anis-a

Lives-in

Is-a

has

has

Has-a is-a

ExampleExampleMammal is a kind of animal that has vertebrata. Cat, Bear and whale are mammal. Cat and Bear has fur. Fish is a type of animal. Whale is a Fish and Fish lives in water.

AdvantagesExplicit in visualization and easy to understand

Often used as a communication tool between the

knowledge engineer and the expert during the knowledge

acquisition phase

SNs are particularly good at representing knowledge in the

form of hierarchies

Knowledge is hierarchically categorized (classified)

Quick inference possible

Supports default reasoning in finite timeApril 18, 2023 21

DisadvantagesNo interpretation standard – Lack well-defined

semantics

They are less reliable than other knowledge

representation techniques because inferring

becomes a process of searching across the

diagram.

Quite limited inference possible

Diagrams can become very complex.April 18, 2023 22

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