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 1
Clyde is an elephant.
Mammal
is-a
Elephant
instance
Clyde
.
Example 2
has
Tail
is-a
Great
Dane
Dog
communicates
Barks
height
Tall
instance
Pluto
has
has 4 Legs
Spots
Example 3
Mammal
is-a
Person
has-a
Nose
instance
Blue
uniform
colour
Pee-Wee team Brooklyn
Dodgers
Reese
Example 4
John’s height is 72.
John
height
72
John is taller than Bill.
John
Bill
height
H1 greater
than
height
H2
Example 5
John gives Mary the book.
Mary
recipient
Give
giver
object
Book32
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
time
Sarah
agent
Fix
object
instrument
past
chair
glue
Exercises
Construct 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
1-ary relation
bird
flies
2-ary relation
dog
colour
brown
3-ary relation
mother
child
parents
father
Example
Mary gave John the book.
person:
Mary
agent
person:
John
agent
give
object
book
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
dog:
Emma
dog:
#1352
colour
brown
colour
brown
Example 2: Unique Marker
dog:
#1352
colour
nam e
brown
”emma”
Example
Her name was McGill and she called herself
Lil, but everyone knew her as Nancy.
name
“McGill”
person:
#941
name
“Lil”
name
”Nancy”
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 Marker
The dog is scratching its ear with its paw.
dog: *X
agent
object
scratch
ear
instrument
part
paw
part
dog: *X
Display Form
John is going to Boston by bus.
person:
John
agent
go
instance
bus
destination
city:
Boston
Linear Form
John is going to Boston by bus.
[Go] –
(Agnt) → [Person: John]
(Dest) → [City: Boston]
(Inst) → [Bus]
Exercises
Construct 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.