What is a Knowledge Representation?
COMP34512
Sebastian Brandt
[email protected]
(slides by Bijan Parsia [email protected])
Tuesday, 25 February 2014
Where are we?
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Tuesday, 25 February 2014
Where are we?
• We’ve been fumbling toward one
– Knowledge Acquisition
• Including Coursework
– Some formalization
– Some thoughts about formalisms
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Tuesday, 25 February 2014
Where are we?
• We’ve been fumbling toward one
– Knowledge Acquisition
• Including Coursework
– Some formalization
– Some thoughts about formalisms
• But what is it that we’re producing?
– For an answer, we turn to a famous paper
• “What is a Knowledge Representation?”
• Randall Davis, Howard Shrobe, and Peter Szolovits (1993)
• http://bit.ly/whatIsA
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Tuesday, 25 February 2014
A question!
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Tuesday, 25 February 2014
A question!
• What is DSS’s definition of a KR?
– It’s not clear that they have one
– It’s not clear that there is one!
– Characterisation rather than definition
• I.e., a framework for thinking about and analysing KRs
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Tuesday, 25 February 2014
A question!
• What is DSS’s definition of a KR?
– It’s not clear that they have one
– It’s not clear that there is one!
– Characterisation rather than definition
• I.e., a framework for thinking about and analysing KRs
• They do so by means of a set of “roles”
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Tuesday, 25 February 2014
Five Roles
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
2. Expression of ontological commitment
– of the world
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
2. Expression of ontological commitment
– of the world
3. Theory of intelligent reasoning
– and our knowledge of it
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
2. Expression of ontological commitment
– of the world
3. Theory of intelligent reasoning
– and our knowledge of it
4. Medium of efficient computation
– that is accessible to programs
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
2. Expression of ontological commitment
– of the world
3. Theory of intelligent reasoning
– and our knowledge of it
4. Medium of efficient computation
– that is accessible to programs
5. Medium of human expression
– and usable
4
Tuesday, 25 February 2014
Five Roles
1. Surrogate
– That is, a representation
2. Expression of ontological commitment
– of the world
3. Theory of intelligent reasoning
– and our knowledge of it
4. Medium of efficient computation
– that is accessible to programs
5. Medium of human expression
– and usable
A KR is a representation of the world and our knowledge
of it that is accessible to programs and usable
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Tuesday, 25 February 2014
A Surrogate
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Tuesday, 25 February 2014
A Surrogate
• Surrogate?
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Tuesday, 25 February 2014
A Surrogate
• Surrogate?
• Representations are abstractions
– No representation captures everything
– It wouldn't be useful it if did!
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Tuesday, 25 February 2014
A Surrogate
• Surrogate?
• Representations are abstractions
– No representation captures everything
– It wouldn't be useful it if did!
• The “goodness” of a representation is context sensitive
and interest relative
– It depends on the applications
– We might trade off
• Accuracy for intelligibility
• Detail for performance
– Other properties might be interest and context independent
– But we always exclude something
• And we may even (deliberately) misrepresent!
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Tuesday, 25 February 2014
A Surrogate
• Surrogate?
• Representations are abstractions
– No representation captures everything
– It wouldn't be useful it if did!
• The “goodness” of a representation is context sensitive
and interest relative
– It depends on the applications
– We might trade off
• Accuracy for intelligibility
• Detail for performance
– Other properties might be interest and context independent
– But we always exclude something
• And we may even (deliberately) misrepresent!
• What does the representation actually represent?
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Tuesday, 25 February 2014
Ontological Commitment
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Tuesday, 25 February 2014
Ontological Commitment
• Imperfection of reps entails choice of what to represent
– And how to
– Even if we captured everything, organisation matters!
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Tuesday, 25 February 2014
Ontological Commitment
• Imperfection of reps entails choice of what to represent
– And how to
– Even if we captured everything, organisation matters!
• Representation is relational
– See surrogacy
– Formalisms (typically) constrain, not determine the relations
• Model theory (as you shall see)
– Early choices constrain future choices
• But not entirely!
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Tuesday, 25 February 2014
Ontological Commitment
• Imperfection of reps entails choice of what to represent
– And how to
– Even if we captured everything, organisation matters!
• Representation is relational
– See surrogacy
– Formalisms (typically) constrain, not determine the relations
• Model theory (as you shall see)
– Early choices constrain future choices
• But not entirely!
• Formal objects vs. “real” objects
– Cat SubClassOf: Animal
– G1 SubClassOf: G2
– What’s the difference?
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Tuesday, 25 February 2014
Taxonomic position
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Tuesday, 25 February 2014
Taxonomic position
• Not just hard, but (perhaps) impossible
– No one hierarchy
• “Discussion of the hierarchies frequently will elicit comments from the
domain expert about the hierarchy structure. Not infrequently in
biomedicine, there is no canonical determination of a concept’s correct
tree position. For example, meningococcal meningitis may be classified
correctly as both a disease of the central nervous systems and a
bacterial disease.” —Modeling a description logic vocabulary for cancer research
– Hierarchies aren’t neutral!
• “In meta-utopia, the lab-coated guardians of epistemology sit down and
rationally map out a hierarchy of ideas...This presumes that there is a
"correct" way of categorizing ideas, and that reasonable people, given
enough time and incentive, can agree on the proper means for building
a hierarchy. Nothing could be farther from the truth. Any hierarchy of
ideas necessarily implies the importance of some axes over others.” —
Metacrap: Putting the torch to seven straw-men of the meta-utopia
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Tuesday, 25 February 2014
Lab Coat View
Mary Van Rensselaer Buell (1893-1969)
http://www.flickr.com/photos/smithsonian/3322785642/
http://www.well.com/~doctorow/metacrap.htm#2.5
Tuesday, 25 February 2014
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Lab Coat View
Mary Van Rensselaer Buell (1893-1969)
http://www.flickr.com/photos/smithsonian/3322785642/
http://www.well.com/~doctorow/metacrap.htm#2.5
Tuesday, 25 February 2014
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Duelling Manufacturers
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Tuesday, 25 February 2014
Duelling Manufacturers
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Tuesday, 25 February 2014
Duelling Manufacturers
vs
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Tuesday, 25 February 2014
Two Views
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Tuesday, 25 February 2014
Two Views
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Tuesday, 25 February 2014
Two Views
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Tuesday, 25 February 2014
Two Views
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Tuesday, 25 February 2014
Two Views
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Tuesday, 25 February 2014
Two Views
(Navigational, not generalisation)
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Tuesday, 25 February 2014
“A KR is not a Data Structure”
• Critical point!
– ER diagrams* -- 4 levels of views of data:
1. "Information concerning [E] and [R] which exist in our minds."
2. "Information structure -- organization of information in which [E] and [R]
are represented by data. "
3. "Access-path-independent data structure -- the data structures which
are not involved with search schemes, indexing schemes, etc."
4. "Access-path-dependent data structure."
–
“the network model, as currently implemented, is mainly
concerned with level 4; the relational model is mainly concerned
with levels 3 and 2; the entity set model is mainly concerned
with levels 1 and 2.”
– The KR model is mainly concerned with level 1
– The “cognitive view”
– Foreshadow role 5 “medium of human expression”
* Chen, The Entity-Relationship Model-Toward a Unified View of Data
Tuesday, 25 February 2014
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Tuesday, 25 February 2014
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Tuesday, 25 February 2014
Data Structures?
• Data structures implement (or realise) representations
– And there is a lot of choice
– Many details of the structures play no representational role
– That is, those details don’t commit
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Tuesday, 25 February 2014
Data Structures?
• Data structures implement (or realise) representations
– And there is a lot of choice
– Many details of the structures play no representational role
– That is, those details don’t commit
• Choices at every level are critical
– But in different ways
– (Foreshadow role 4 “medium of efficient computation”)
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Tuesday, 25 February 2014
Intelligent Reasoning
• Representation and reasoning are correlative
– Tendentious, but reasonable
– Representation without manipulation (or manipulability)
• isn't a representation
• If you can't use it to acquire information, in what sense does it
represent?
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Tuesday, 25 February 2014
Intelligent Reasoning
• Representation and reasoning are correlative
– Tendentious, but reasonable
– Representation without manipulation (or manipulability)
• isn't a representation
• If you can't use it to acquire information, in what sense does it
represent?
• Components
– Fundamental conception
• Deduction, human behavior, etc. etc.
– Sanctioned inferences
– Recommended inferences
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Tuesday, 25 February 2014
Intelligent Reasoning
• Representation and reasoning are correlative
– Tendentious, but reasonable
– Representation without manipulation (or manipulability)
• isn't a representation
• If you can't use it to acquire information, in what sense does it
represent?
• Components
– Fundamental conception
• Deduction, human behavior, etc. etc.
– Sanctioned inferences
– Recommended inferences
• There are many many many formalisms
– With different fundamental conceptions
– Model theory (we shall see) is pretty unifying
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Tuesday, 25 February 2014
Strong Cognitive Adequacy
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Tuesday, 25 February 2014
Strong Cognitive Adequacy
• Should the conception be a model of human reasoning?
– Usually associated with the psychological or neuroscience or
commonsense reasoning traditions
– KRs can help us understand human intelligence
– Flip side, since we are the most successful cognitive agents we
know, aping us might be successful
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Tuesday, 25 February 2014
Efficient Computation
• Programs have to work with representations
– The representation management system is a component
– Programmers will compensate for inefficient components
– (Strong Cognitive Adequacy to Efficient Computation fallacy)
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Tuesday, 25 February 2014
Efficient Computation
• Programs have to work with representations
– The representation management system is a component
– Programmers will compensate for inefficient components
– (Strong Cognitive Adequacy to Efficient Computation fallacy)
• Most interesting systems work at “large” scale
– Consider databases
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Tuesday, 25 February 2014
Efficient Computation
• Programs have to work with representations
– The representation management system is a component
– Programmers will compensate for inefficient components
– (Strong Cognitive Adequacy to Efficient Computation fallacy)
• Most interesting systems work at “large” scale
– Consider databases
• Representations get complex quickly
– People need prosthetics to work well with them
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Tuesday, 25 February 2014
Human Expression
• Humans interact with representations
– Effectively
– At least of certain kinds
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Tuesday, 25 February 2014
Human Expression
• Humans interact with representations
– Effectively
– At least of certain kinds
• People must work with KRs
– Generating them
– Using them to build systems
– Using them when using the system
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Tuesday, 25 February 2014
Human Expression
• Humans interact with representations
– Effectively
– At least of certain kinds
• People must work with KRs
– Generating them
– Using them to build systems
– Using them when using the system
• Weak Cognitive Adequacy
– KRs must be usable
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Tuesday, 25 February 2014
Five Roles
1. Surrogate
Representing
– That is, a representation
2. Expression of ontological commitment
– of the world
3. Theory of intelligent reasoning
– and our knowledge of it
4. Medium of efficient computation
– that is accessible to programs
5. Medium of human expression
Computing
– and usable
Interacting
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Tuesday, 25 February 2014