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Transcript of Contents Knowledge Representation Rule-Based Representation Frame-Based Representation ...
Contents
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
April 18, 2023 4
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.
April 18, 2023 5
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?
April 18, 2023 6
CLASS: Vehicle
CLASS: Boat CLASS: CarCLASS: Airplane
is-a is-a is-a
Superclass: Vehicle
Superclass: Vehicle
Superclass: Vehicle
Generalization
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
April 18, 2023 7
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.
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
How are objects related in a frame-based system?
April 18, 2023 8
CLASS: Car
CLASS:Chassis CLASS:Engine CLASS:Transmission
a-part-of
Superclass: Car Superclass:Car Superclass:Car
Aggregation
a-part-of a-part-of
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
April 18, 2023 9
Association:It describes some semantic relationship
between different classes which are unrelated otherwise.
For example, Mr. Black owns a car.
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
How are objects related in a frame-based system?
April 18, 2023 10
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
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
April 18, 2023 11
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.
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
Advantages
April 18, 2023 12
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.
Frame-Based Knowledge Frame-Based Knowledge RepresentationRepresentation
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
April 18, 2023 13
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.
April 18, 2023 14
ExampleDraw a diagram representing the relationships between
Mary and Joe, indicating the relationship between a trainer, consultant, programmer and employee.
April 18, 2023 15
ExampleSuch a diagram is the beginning of a semantic
network but this can be improved by more closely defining the nature of the relationships.
April 18, 2023 16
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
April 18, 2023 18
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.
April 18, 2023 19
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