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Knowledge Representation. Introduction. Domain specific knowledg e is needed to solve some problems. Knowledge base – representation. Inference techniques Use to prove facts. Use to answer queries. Knowledge Representation Schemes. - PowerPoint PPT Presentation
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Knowledge Representation
Introduction
• Domain specific knowledge is needed to solve some problems.
• Knowledge base – representation.• Inference techniques• Use to prove facts.• Use to answer queries
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.
.
Semantic Networks
• Consists of nodes and arcs.• Nodes represents objects.• Arcs represents relationships between the
objects.• Relationships:
– is-a – Instance– has/has-a– Others
.
Example 1Clyde is an elephant.
.
Mammal
Elephant
Clyde
is-a
instance
Example 2
Tail Dog 4 Legs
GreatDane Barks
Tall
Pluto Spots
has has
is-a communicates
heightinstance
has
Example 3
Mammal
Person Nose
Pee-Wee BrooklynBlue Reese Dodgers
is-a
has-a
instance
teamuniformcolour
Example 4
John’s height is 72.
John is taller than Bill.
John 72height
John
H1
Bill
H2
height height
greaterthan
Example 5John gives Mary the book.
Give
Book32
recipient
object
giverMary John
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..
Example: Case Frame
glue
Fix
instrument
time
objectagentSarah
past
chair
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.
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.
Conceptual Graph Relations
bird flies
dog colour brown
child parents
mother
father
1-ary relation
2-ary relation
3-ary relation
ExampleMary gave John the book.
Maryagent
agent
give object
book
person:
person:John
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.
Example 1: Unique Markers
Emmacolour brown dog:
#1352colour brown dog:
Example 2: Unique Marker
name ”emma”
#1352colour brown dog:
Example Her name was McGill and she called herself Lil,
but everyone knew her as Nancy.
name ”Nancy”
#941name
“McGill”
person: name
“Lil”
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.
Example: Generic MarkerThe dog is scratching its ear with its paw.
objectagent scratch
instrument
dog: *X
paw
ear
dog: *X
part
part
Display FormJohn is going to Boston by bus.
agentperson:John go destination
city:Boston
instance
bus
Linear Form
[Go] –(Agnt) → [Person: John](Dest) → [City: Boston](Inst) → [Bus]
John is going to Boston by bus.
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.