week2 intro knowledge representation

7/24/2019 Week2 Intro Knowledge Representation

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Artificial Intelligence CS364Artificial Intelligence CS364

Knowledge RepresentationKnowledge Representation

Lectures on Artificial Intelligence CS364Lectures on Artificial Intelligence CS364

Introduction toIntroduction to Knowledge RepresentationKnowledge Representation

13thSeptember 2!

Dr Bogdan L. rusias!."rusias#surre$.ac.u%


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ContentsContents

( )efining Knowledge Representation

( Knowledge Representation Schemes

( Semantic *etwor+s

( ,a-onom.( /ntolog.


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( 0A representationis a set of conentions abo&t how to

describe a class of things$ A description ma+es &se of the

conentions of a representation to describe some partic&lar

thing$0 inston 12516$

( 07ood representations ma+e important ob8ects and relations

e-plicit9 e-pose nat&ral constraints9 and bring ob8ects and

relations together0 ibid5 4!

( ,he representation principle5

/nce a problem is described &sing an appropriate representation9

the problem is almost soled$


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Starting wit& an '(a)pleStarting wit& an '(a)ple

( ,he :armer9 ,he :o-9 ,he 7oose and ,he 7rain5

,he farmer m&st get a fo-9 a goose and a sac+ of grain across a

rier9 howeer his boat is small and he can onl. carr. one thing at

a time$ ;is problem is that if he leaes the fo- with the goose the

goose will be eaten9 and if he leaes the goose with the grain9 thegrain will be eaten


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7rain

:o-

:armer

7oose

:armer

7oose

7rain

:o-

:armer

:o-7oose

7rain

:o-

7rain

:armer

7oose

:armer

:o-7rain

7oose

7oose

:armer

:o-

7rain

:armer

7oose

:o-

7rain

:armer

7oose

:o-

7rain

:o-

:armer

7oose

7rain

:armer

:o-

7oose

7rain


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Knowledge Representation Sc&e)esKnowledge Representation Sc&e)es

( A n&mber of +nowledge representation schemes or formalisms hae

been &sed to represent the +nowledge of h&mans in a s.stematic

manner$ ,his +nowledge is represented in a %nowledge !ases&ch that

it can be retrieed for soling problems$ Amongst the well?established

+nowledge representation schemes are5

=rod&ction R&les

Semantic *etwor+s

:rames

Concept&al )ependenc. 7rammar

Concept&al 7raphs

/ntolog.

=redicate and @odal #ogic

Concept&al or ,erminological #ogics

@# B R):


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Se)antic *etwor%sSe)antic *etwor%s

( Ross D&illian 166 and 16E was among the earl. AI

wor+ers to deelop a comp&tational model which

represented 0concepts0 as &ierarc&icalnetwor+s$

( ,his model was amended with some additional

ps.chological ass&mptions to characterise the str&ct&re of

Fh&manG semantic memor.$


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( Collins and D&illian 16 proposed that5

Concepts can be represented as hierarchies of inter?

connected concept nodes e$g$ animal9 bird9 canar.

An. concept has a n&mber of associated attrib&tes at a gien leel

e$g$ animal ??H has s+in eats etc$

Some concept nodes are superordinatesof other nodes e$g$animal H bird and some are su!ordinatescanar. J bird


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( :or reasons of cogniti"e econo)$9 s&bordinates in&erit

all the attrib&tes of their s&perordinate concepts$

( Some instances of a concept are e(ceptedfrom the

attrib&tes that help Fh&mansG to define the s&perordinates

e$g$ ostrich is e-cepted from fl.ing

( %ario&s Fps.chologicalG processes searc&these hierarchies

for information abo&t the concepts represented$


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Se)antic *etwor% '(a)pleSe)antic *etwor% '(a)ple

birdcan fl.9 &as wings9

&as feathers

salmonlayseggsswims&pstream9

ispin+9 isedible

ostrichrunsfast9 cannotfly9

istall

canar.can sing9 is.ellow

fishcan swim9 &as fins9 &as gills

ani)alcanbreathe9 caneat9

&as s+in

is+a

is+a

is+a

is+a

is+a


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Se)antic *etwor% '(a)pleSe)antic *etwor% '(a)ple

( :rom the aboe ta-onomic organisation of +nowledge abo&t a n&mber

of different animals9 one can concl&de9 b. 0in&eriting properties

down t&e ta(ono)$09 that canaries9 ostriches and salmon all hae s+in

and can breathe$

( "&t we as h&mans can also ma+e e(ceptionsto inherited properties in

that we can represent an not?fl.ing bird in a s&b? hierarch. of birds

b. simpl. noting the e-ception9 can't fly$

( Collins and D&illian carried o&t a n&mber of tests on h&man s&b8ectsand fo&nd that the s&b8ects recognise propositions lower down the

hierarch. canar. is a .ellow bird more readil. than propositions

higher &p the hierarch. canar. has s+in$


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Defining In&eritanceDefining In&eritance

( AI researchers hae refined the notion of inheritance5

It is called a specialised inferencing techni&e 0for representing

properties of classes9 e-ceptions to inherited properties9 m&ltiple

s&perclasses9 and str&ct&red concepts with specific relationsamong the str&ct&ral elements0 ,o&retL+. 1256$


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( A semantic networ+ is a str&ct&re for representing +nowledge as a

pattern of interconnected nodesand arcs$ *odes in the net represent

conceptsof entities9 attrib&tes9 eents9 al&es$ Arcs in the networ+

represent relations&ipsthat hold between the concepts$

( A semantic networ+ is a graph theoretic data str&ct&re whose nodes

represent word senses and whose arcs e-press se)antic relations&ips

between these word senses$

( D&illian gae an acco&nt9 perhaps first &sed b. a comp&ter scientist9 ofthe associate feat&res of h&man memor. that incorporated a spreading

actiation model of comp&tation$


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*etwor%s and ,-eaning, Representation*etwor%s and ,-eaning, Representation

( ,he bios.stematic notions of ta(ono)ies9 where the

concept of s&perordinates and s&bordinates pla.s a ma8or

role on the +nowledge representation literat&re$

( ,A/*/@M /: #I:N5 ,he ta-onomic organisation of

species in a hierarchical str&ct&re5 Kingdom H =h.l&m diision in botan. H Class H /rder H :amil.

H 7en&s H Species

( Carol&s #innea&s c$1Eth cent&r. Swedish botanist

deised the s.stem of binomial nomenclat&re &sed fornaming species5

each species has a two?part #atin name9 formed b. appending a

specific epithet to the gen&s name$

,he latter is capitalised and both parts italicised$


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D/ S0/AR-A1L'

BR'AD-0LD

I*2'S2I*ALBAC2'RI0-

1*D AL/A'

KI*/D- Animaliaanimals

=lantae plants :&ngi f&ngi =ro+ar.otaebacteria

=rotoctista algae9protoLoa9 slimmo&lds

1L0- Chordata @agnolioph.ta O.gom.cota /mnibacteria Chloroph.ta

CLASS @ammalia Rosidae O.gom.cetes Nnterobacteria N&con8&gatae

RD'R Carniora Sapindales @acorales N&bacteriales O.gnematales

5A-IL Canidae Aceraceae @&coraceae E. colidoes not&a"e a fa)il$

classification7

O.gnemataceae

/'*0S Canis Acer Rhizopus Escherichia Spirogyra

S1'CI'S C. familiaris A.saccharum R. stolonifer E. Coli S. crassa

-odern 2a(ono)$ '(a)ple-odern 2a(ono)$ '(a)ple


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Representation and Bios$ste)aticsRepresentation and Bios$ste)atics

( or+ in +nowledge representation has been infl&enced b.

+e. notions in bios.stematics$

( ;oweer9 there are cr&cial differences between what a

ta-onomist does and a +nowledge engineer does$

( ,he +e. difference is that of the intended a&dience in the

two cases5

for the ta-onomist the a&dience is intelligent and h&man

and for the +nowledge engineer the primar. 0a&dience0 is a

comp&ter s.stem9 or more acc&ratel. the representation program$

A ifi i l lli CS364


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ntolog$ntolog$

( )efinition5

P,he science or st&d. of being that department of metaph.sics

which relates to the being or essence of things9 or to being in the

abstract$Q /N) online9 http5BBwww$oed$comB

ifi i l lliA ifi i l I lli CS364


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ntolog$ntolog$

( AI e-perts9 li+e ,om 7r&ber9 s&ggest that5

0In the conte-t of +nowledge sharing9 I &se the term ontolog. to

mean aspecification of a conceptualization$ ,hat is9 an ontolog. is

a description li+e a formal specification of a program of the

concepts and relationships that can e-ist for an agent or a

comm&nit. of agents$ ,his definition is consistent with the &sage

of ontolog. as set?of?concept?definitions9 b&t more general$ And it

is certainl. a different sense of the word than its &se in

philosoph.$0 Cited from www?+sl$stanford$ed&B+stBwhat?is?an?

ontolog.$html site isited 12BB!

A ifi i l I lli CS364A ifi i l I lli CS364


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ntolog$ntolog$

( Also ,om 7r&ber9 s&ggest that5

0An ontolog. is an e-plicit specification of a concept&aliLation$ ,he term

is borrowed from philosoph.9 where an /ntolog. is a s.stematic acco&nt

of N-istence$ :or AI s.stems9 what e-ists is that which can be

represented$ hen the +nowledge of a domain is represented in a

declaratie formalism9 the set of ob8ects that can be represented is calledthe uni"erse of discourse$ ,his set of ob8ects9 and the describable

relationships among them9 are reflected in the representational ocab&lar.

with which a +nowledge?based program represents +nowledge$ ,h&s9 in

the conte-t of AI9 we can describe the ontolog. of a program b. defining

a set of representational terms$ In s&ch an ontolog.9 definitions associate

the names of entities in the &nierse of disco&rse e$g$9 classes9 relations9f&nctions9 or other ob8ects with h&man?readable te-t describing what the

names mean9 and formal a-ioms that constrain the interpretation and well?

formed &se of these terms$ :ormall.9 an ontolog. is the statement of a

logical theor.$0 Cited from www?+sl$stanford$ed&B+stBwhat?is?an?

ontolog.$html site isited 12BB!

A ifi i l I lli CS364A tifi i l I t lli CS364


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ntolog$ as a Specification -ec&anis)ntolog$ as a Specification -ec&anis)

( A bod. of formall. represented +nowledge is based on a

conceptuali8ation5 the ob8ects9 concepts9 and other entities

that are ass&med to e-ist in some area of interest and the

relationships that hold among them 7enesereth T

*ilsson9 1E$( A concept&aliLation is an abstract9 simplified iew of the

world that we wish to represent for some p&rpose$

( Ner. +nowledge base9 +nowledge?based s.stem9 or

+nowledge?leel agent is committed to someconcept&aliLation9 e-plicitl. or implicitl.$

A tifi i l I t lli CS364A tifi i l I t lli CS364


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ntolog$ntolog$

A tifi i l I t lli CS364A tifi i l I t lli CS364


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ClosingClosing

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( Remar+sUUU

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week2 intro knowledge representation

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