1. Knowledge Representation Techniques
CHAPTER 2
Knowledge Representation Techniques
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2. DEFINITION AND SCOPE OF KNOWLEDGE
Knowledge is available from many sources,
some of which are documented, and others
are undocumented (experts).
Knowledge can be shallow, describing a
narrow input-output relationship, or deep,
describing complex interactions and a
system’s operation.
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3. DEFINITION AND SCOPE OF KNOWLEDGE
Knowledge acquisition can be difficult because of the scope of knowledge and several communication and processing problems.
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4. OBJECT ATTRIBUTE TRIPLETS
OBJECT-ATTRIBUTES-VALUE-TRIPLETS (OAV)
In expert system, facts is often referred to as
proposition. Proposition is a statement that
is either true or false. e.g. It is raining.
Truth value of this statement is TRUE or
FALSE Can be easily represented in O-A-V.,
which is a more complex type of proposition.
Divide into 3 distinct part: object, attributes
and values; The table on the next slide
present some O-A-V triplets :
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5. OBJECT ATTRIBUTE TRIPLETS (OAV)
Attributes
Values
House
Bedrooms
2,3,4 etc
Colour
Blue, yellow
Admission_to university
GPA
3.0, 3.5
Inventory control
Level_of inventory
15, 20, 30
Bedroom
Size
9’X10’, 6’X12’
Fact : The make of the car is Honda
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6. OBJECT ATTRIBUTE TRIPLETS
Object can be:
·      physical item, such as car, ball etc
·      abstract item such as admission to university
Attribute is the property or feature of the object.
Value specifies the attribute assignment. It can be
boolean, string or numeric.
Object can have more than one attributes i.e.
Multiple attributes
Sometimes a certainty factor is added to the triplet
in order to measure its degree of certainty.
CF is a numeric value assigned to a statement that
represent the degree of disbelief in the statement .
Ranges from -1 (definitely false) to +1 (definitely
true) For e.g., “It will probably rain today”, can
assign CF of 0.6.
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7. OBJECT ATTRIBUTE TRIPLETS (OAV)
This is one of the attitudes towards Expert
Systems. By using a card sort study, OAV
can be one of the ES to help to improve the
difficult situation of making a diagnosis in
podiatry, easing chiropodist’s job.
Card Methodology may be a useful technique
to explore attitudes towards the use of expert
systems within a domain.
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8. SEMANTIC NETWORKS
The simplest kind of structured object is the semantic network originally developed in the early 1960s.They are important both historically, and in introducing the basic ideas of class hierarchies and inheritance.
A semantic network is really just a graph, where the nodes in the graph represent concepts, and the arcs represent binary relationships between concepts.
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9. PRODUCTION RULES A form of procedural knowledge that
describes how to solve a problem. The
procedural and/or factual knowledge is
represented as rules, called productions, in
the form of condition-action pairs.
Is stated as follows: "IF this condition
occurs, THEN do this action; or this result (or
conclusion or consequence) will occur. For
E.g. : IF flammable liquid was spilled,        
THEN call the fire department.
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10. FRAMES
Frames  are descriptions of conceptual individuals. Frames can exist for ``real'' objects such as ``The Watergate Hotel'', sets of objects such as ``Hotels'', or more ``abstract'' objects such as ``Cola-Wars'' or ``Watergate'‘
Frames are essentially defined by their relationships with other frames
Relationships between frames are represented using slots
If a frame f is in a relationship r to a frame g, then we put the value g in the r slot of f
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11. FRAMES
A script is a type of frame that describes what happens temporally; the usual example given is that of describing going to a restaurant
The steps include waiting to be seated, receiving a menu, ordering, etc.
Frames are also powerful knowledge representation system that are accessible to both humans and machine. A frame is a collection of information and associated actions that represents a simple concept.
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12. LOGICAL EXPRESSIONS PROPOSITIONAL LOGIC (P.L.)
Propositional logic represents and reasons with propositions.
P.L. assigns symbolic variable to a proposition such as
A = The car will start
In. P. L. if we are concern with the truth of the statement, we will check the truth of A.
Logic Operators and symbols:
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13. PROPOSITIONAL LOGIC Operators Symbols AND Ù, &, Ç OR Ú, È, + NOT Ø, ~
IMPLIES
É, ®
EQUIVALENT
Propositions that are linked together with
connectives, e.g. AND, OR, NOT, IMPLIES, and
EQUIVALENT, are called compound statements.
Prepositional logic is concerned with the
truthfulness of compound statements, depending
on the connectives.
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14. LOGICAL EXPRESSIONS Predicate Calculus
The predicate calculus includes a wider range of entities
It permits the description of relations and the use of variables.
It also requires an understanding of quantification
The language of predicate calculus requires:
Variables and Constants
---these include the logical constants
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15. MULTIPLE KNOWLEDGE REPRESENTATION
In cognitive science knowledge representation is concerned with how people store and process information.
In Artificial Intelligence (AI) the primary aim is to store knowledge so that programs can process it and achieve the verisimilitude of human intelligence
AI researchers have borrowed representation theories from cognitive science
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16. MULTIPLE KNOWLEDGE REPRESENTATION
Thus there are representation techniques such as frames, rules and semantic networks which have originated from theories of human information processing
Since knowledge is used to achieve intelligent behavior, the fundamental goal of knowledge representation is to represent knowledge in a manner as to facilitate inferencing i.e. drawing conclusions from knowledge
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17. MULTIPLE KNOWLEDGE REPRESENTATION
Some issues that arise in knowledge representation from an AI perspective are:
How do people represent knowledge?
What is the nature of knowledge and how do we represent it?
Should a representation scheme deal with a particular domain or should it be general purpose?
Should the scheme be declarative or procedural?
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