Knowledge Representation
description
Transcript of Knowledge Representation
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Knowledge Representation
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Introduction
• Domain specific knowledge is needed to solve some problems.
• Knowledge base – representation.• Inference techniques• Use to prove facts.• Use to answer queries
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Knowledge Representation Schemes
• Logical representation schemes – logical proofs, e.g. predicate logic.
• Procedural representation schemes – procedural list of instructions, e.g. production rule systems.
• Network representation schemes – graphical representation, e.g. semantic networks and conceptual graphs.
• Structured representation schemes –extension of network schemes, e.g. scripts and frames.
• Structures for incomplete or inconsistent knowledge: Bayesian reasoning, Dempster-Shafer, fuzzy logic.
.
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Semantic Networks
• Consists of nodes and arcs.• Nodes represents objects.• Arcs represents relationships between the
objects.• Relationships:
– is-a – Instance– has/has-a– Others
.
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Example 1Clyde is an elephant.
.
Mammal
Elephant
Clyde
is-a
instance
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Example 2
Tail Dog 4 Legs
GreatDane Barks
Tall
Pluto Spots
has has
is-a communicates
heightinstance
has
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Example 3
Mammal
Person Nose
Pee-Wee BrooklynBlue Reese Dodgers
is-a
has-a
instance
teamuniformcolour
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Example 4
John’s height is 72.
John is taller than Bill.
John 72height
John
H1
Bill
H2
height height
greaterthan
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Example 5John gives Mary the book.
Give
Book32
recipient
object
giverMary John
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Using Case Frames
• Problems with semantic networks• Attempts to standardize semantic networks
led to the development of case frames.• Each sentence is represented by a case
frame.• Each case frame represents an actions.• Case frames define case relationships: agent,
object, instrument, location and time..
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Example: Case Frame
glue
Fix
instrument
time
objectagentSarah
past
chair
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ExercisesConstruct semantic networks for the following statements:• Pompeian(Marcus), Blacksmith(Marcus). • Mary gave the green coloured vase to
her favorite cousin.• John went downtown to deposit his
money in a bank.
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Conceptual Graphs
• Is a connected bipartite graph.• Conceptual relation nodes represent
relations between concepts. • The arcs connecting nodes are not
labeled.• Concepts are represented by boxes.• Relations are represented by arcs.
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Conceptual Graph Relations
bird flies
dog colour brown
child parents
mother
father
1-ary relation
2-ary relation
3-ary relation
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ExampleMary gave John the book.
Maryagent
agent
give object
book
person:
person:John
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Unique Markers
• If an individual object is unknown a unique marker can be used in place of the name of the object.
• A unique marker is comprised of a hash symbol (#) followed by a number.
• Each object has its own unique marker.
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Example 1: Unique Markers
Emmacolour brown dog:
#1352colour brown dog:
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Example 2: Unique Marker
name ”emma”
#1352colour brown dog:
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Example Her name was McGill and she called herself Lil,
but everyone knew her as Nancy.
name ”Nancy”
#941name
“McGill”
person: name
“Lil”
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Generic Markers
• A generic marker is used to represent an unspecified individual of a type.
• A generic marker is represented by an asterisk *.
• Name variables can also be used, e.g., *X to indicate an unspecified individual.
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Example: Generic MarkerThe dog is scratching its ear with its paw.
objectagent scratch
instrument
dog: *X
paw
ear
dog: *X
part
part
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Display FormJohn is going to Boston by bus.
agentperson:John go destination
city:Boston
instance
bus
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Linear Form
[Go] –(Agnt) → [Person: John](Dest) → [City: Boston](Inst) → [Bus]
John is going to Boston by bus.
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ExercisesConstruct conceptual graphs for the following statements:• Jane gave Tom an ice cream.• Basketball players are tall.• Paul cut down the tree with an axe.• Place all the ingredients in a bowl and
mix thoroughly.