artificial intelligence
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Artificial Intelligence. Contents. Knowledge Representation Rule-Based Representation Frame-Based Representation Semantic-Networks. What is frame? A frame is a data structure with typical knowledge about a particular object or concept. - PowerPoint PPT PresentationTRANSCRIPT
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Artificial Intelligence
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Contents
Knowledge Representation Rule-Based Representation Frame-Based Representation Semantic-Networks
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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.
How are objects related in a frame-based system?
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CLASS: Vehicle
CLASS: Boat CLASS: Car CLASS: 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.
How are objects related in a frame-based system?
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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 relationship between
different classes which are unrelated otherwise.
For example, Mr. Black owns a car.
How are objects related in a frame-based system?
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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
Frame-Based Knowledge Representation
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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.
Frame-Based Knowledge RepresentationAdvantages
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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.
Frame-Based Knowledge RepresentationDisadvantages
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Semantic NetworkSN was first proposed by Quillian in 1966, as a model of human
memory
Semantic network (SN) is a graph-based representation
It is a directed graph
A SN is a network of nodes and links to represent the definition
of a concept (or a collection of concepts)
The nodes represent concepts
The links represent the relations between concepts
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Semantic NetworkIn these networks, objects are shown by nodes, and links
between the nodes describe
the 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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Inheritance
Inheritance 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.
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Inheritance
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Inheritance
You 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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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
ExampleMammal 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.
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Advantages
Explicit 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 time
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Disadvantages
No 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.
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