What is a Knowledge Representation? COMP34512 Sebastian Brandt brandt@cs.manchester.ac.uk (slides by Bijan Parsia bparsia@cs.man.ac.uk) Tuesday, 25 February 2014
Where are we? 2 Tuesday, 25 February 2014
Where are we? • We’ve been fumbling toward one – Knowledge Acquisition • Including Coursework – Some formalization – Some thoughts about formalisms 2 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 2 Tuesday, 25 February 2014
A question! 3 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 3 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” 3 Tuesday, 25 February 2014
Five Roles 4 Tuesday, 25 February 2014
Five Roles 1. Surrogate – That is, a representation 4 Tuesday, 25 February 2014
Five Roles 1. Surrogate – That is, a representation 2. Expression of ontological commitment – of the world 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 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 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 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 4 Tuesday, 25 February 2014
A Surrogate 5 Tuesday, 25 February 2014
A Surrogate • Surrogate? 5 Tuesday, 25 February 2014
A Surrogate • Surrogate? • Representations are abstractions – No representation captures everything – It wouldn't be useful it if did! 5 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! 5 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? 5 Tuesday, 25 February 2014
Ontological Commitment 6 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! 6 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! 6 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? 6 Tuesday, 25 February 2014
Taxonomic position 7 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 7 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 8 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 8 Tuesday, 25 February 2014
Duelling Manufacturers 9 Tuesday, 25 February 2014
Duelling Manufacturers 9 Tuesday, 25 February 2014
Duelling Manufacturers vs 9 Tuesday, 25 February 2014
Two Views 10 Tuesday, 25 February 2014
Two Views 10 Tuesday, 25 February 2014
Two Views 10 Tuesday, 25 February 2014
Two Views 10 Tuesday, 25 February 2014
Two Views 10 Tuesday, 25 February 2014
Two Views (Navigational, not generalisation) 10 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 11 Tuesday, 25 February 2014
12 Tuesday, 25 February 2014
12 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 13 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”) 13 Tuesday, 25 February 2014
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