Web Systems and Algorithms

grotesqueoperationInternet και Εφαρμογές Web

21 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

76 εμφανίσεις

WebSystemsandAlgorithms
OWL
ChrisBrooks
DepartmentofComputerScience
UniversityofSanFrancisco
DepartmentofComputerScienceUniversityofSanFranciscop.1/??
RDFReview
RDFallowsustomakestatementsaboutresources
Statementsarebinarypredicates:
Subject
Property
Value
RDFSallowsustospecifyclassesandproperties
ProvidessupportforOOmodeling
DepartmentofComputerScienceUniversityofSanFranciscop.2/??
AutomatedReasoning
RDFisoneofanumberoflanguagesthatallowfor
automatedreasoning.
Thingsanautomatedreasonercandoinclude:
Consistencychecking
Classication
Detectionofequivalences
Discoveryofclassmembership
DepartmentofComputerScienceUniversityofSanFranciscop.3/??
Whyisautomatedreasoninguseful?
Allowsustoautomaticallyverifylargeontologies
Meansoferrorchecking
Candetectunintendedrelationships
Canintegrateandshareontologies
DepartmentofComputerScienceUniversityofSanFranciscop.4/??
OntologyLanguages
Therehavebeenanumberofdifferentontology
languagesdeveloped.
Goal:Developalanguagethatmapsontoanexisting
logic
Providesucientexpressivity
Well-understoodsemanticsandcomplexity
Thereisafundamentaltradeoffinknowledge
representationbetweenexpressivity(whatitispossible
tosay)andcomplexity(howdifcultitistoperform
inferenceinthislanguage).
DepartmentofComputerScienceUniversityofSanFranciscop.5/??
RDF
SowhatsortsofthingsdoesRDFnotallowustosay?
DepartmentofComputerScienceUniversityofSanFranciscop.6/??
RDF
Localscope-wecan'tdenetherangeofaproperty
differentlydependingonthedomain.
Disjointnessofclasses
Booleancombinationsofclasses
Cardinalityrestrictions
Propertycharacteristics
Transivity,inverse,uniqueness
DepartmentofComputerScienceUniversityofSanFranciscop.7/??
ExpressivityvsComputability
Itmightbetemptingtoaddeveryfeaturewecouldthink
oftoourontologylanguage.
Thiswouldletusexpressawiderangeoffacts.
Ifourlanguageistooexpressive,inferencebecomes
undecidable.
Wewanttobeasexpressiveasnecessary,andno
more.
DepartmentofComputerScienceUniversityofSanFranciscop.8/??
OWL
OWL(WebOntologyLanguage)isafamilyofthree
languagesunderdevelopmentbytheW3C(among
others)
Goal:providemoreexpressivitythanRDFwhile
leaveraging(asmuchaspossible)existingSemantic
Webtechnologies
Threeavors:
OWLfull
OWLDL
OWLLite
DepartmentofComputerScienceUniversityofSanFranciscop.9/??
OWLFull
OWLFullusesallOWLprimitives,andallowsthemto
beappliedtoanyRDF/RDFSresource.
Forexample,youcancreateclassesofclasses,or
restrictthenumberofclassesthatexist.
OwlFullisundecidable
Nocompleteorefcientreasoningsupport
Mostlyinterestingasatheoreticalmodel
DepartmentofComputerScienceUniversityofSanFranciscop.10/??
OWLDL
OWLDLisasubsetofOWLFull
DoesnotallowOWLconstructorstobeappliedto
eachother
OWLDLiscompleteanddecidable
Correspondstowell-knowndescriptionlogics.
Descriptionlogicsdeneconcepts,roles,and
individuals
Fastreasoningenginesalreadyexistforthem.
OWLDListhemostcommonly-usedavor.
DepartmentofComputerScienceUniversityofSanFranciscop.11/??
OWLLite
OWLLiteisevensimpler
Nodisjointness
Cardinalityonly0or1
Noenumeratedclasses
Simplertounderstandandworkwith,butlimited
expressiveness.
DepartmentofComputerScienceUniversityofSanFranciscop.12/??
Compatibility
AllOWLlanguagesareupwardcompatible
EveryOWLLiteontologyisanOWLDLontology
OnlyOWLFullisastrictsupersetofRDF
OtherOWLsdonotallowsomelegalRDFstatements.
DepartmentofComputerScienceUniversityofSanFranciscop.13/??
RDFinOWL
AllOWLavorsuseRDFfortheirsyntax.
AswithRDF,otherformshavebeenintroduced.
InstancesaredeclaredasinRDF.
OWLtypesandcontructorsarespecializationsofRDF.
DepartmentofComputerScienceUniversityofSanFranciscop.14/??
OWLClasses
owl:Classisasubclassofrdfs:Class
<owl:Classrdf:about=''#associateProfessor''>
<owl:disjointWithrdf:resource=''#professor''/>
<owl:disjointWithrdf:resource=''#assistantProfessor''/>
</owl:Class>
DepartmentofComputerScienceUniversityofSanFranciscop.15/??
OWLProperties
OWLcontainstwotypesofproperties:
Objectproperties,whichrelateobjectstoother
objects.
Datatypeproperties,whichrelateobjectstoliterals
TheseuseXMLSchemadatatypes
DepartmentofComputerScienceUniversityofSanFranciscop.16/??
DatatypeProperties
<owl:DatatypePropertyrdf:ID=''age''>
<rdfs:range
rdf:resource=''http://www.w3.org/2001/XMLSchema#nonNegativeInteger''
/>
</owl:DatatypeProperty>
DepartmentofComputerScienceUniversityofSanFranciscop.17/??
ObjectProperties
<owlObjectPropertyrdf:ID=''teaches''>
<owl:domainrdf:resource=#professor''/>
<owl:rangerdf:resource=''#course''>
</owl:ObjectProperty>
DepartmentofComputerScienceUniversityofSanFranciscop.18/??
InverseProperties
<owlObjectPropertyrdf:ID=''isTaughtBy''>
<owl:domainrdf:resource=#course''/>
<owl:rangerdf:resource=''#professor''>
<owl:inverseOfrdf:resource=''#teaches''/>
</owl:ObjectProperty>
AreasonercanusethistodeterminethatifAteachesB,
BistaughtbyA.
DepartmentofComputerScienceUniversityofSanFranciscop.19/??
PropertyRestrictions
AninterestingfeatureofOWListhepropertyrestriction.
Wecanusethistocreatesubclassesofaclassthat
satisfyaspecicproperty.
Forexample,let'ssaywewanttoindicatethatCS
classesareclassesthataretaughtbyCSProfs.
<owl:Classrdf:about=''#CSClass''>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onPropertyrdf:resource=''#isTaughtBy''/>
<owl:allValuesFromrdf:resource=''CSProf''/>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
DepartmentofComputerScienceUniversityofSanFranciscop.20/??
PropertyRestrictions
WhatthisdoesiscreateasubclasscalledCSClass.
itconsistsofallobjectsintherangeoftheisTaughtBy
property(classes)thatarealsoCSProfs.
Wecanalsocreatesubclassesofmultipleclassesthis
way-notethatweneverhavetospecify(orknow)about
theclassclass.
DepartmentofComputerScienceUniversityofSanFranciscop.21/??
PropertyRestrictions
hasValueandsomeValuesFromworksimilarly
Wecanalsousecardinalitytocreatesubclasses.
<owl:Classrdf:about=''#CSClass''>
<rdfs:subClassOf>
<owl:Restriction>
<owl:onPropertyrdf:resource=''#isTaughtBy''/>
<owl:cardinalityrdf:datatype=''&xsd;nonNegativeInteger>1
</owl:cardinality>
</owl:Restriction>
</rdfs:subClassOf>
</owl:Class>
DepartmentofComputerScienceUniversityofSanFranciscop.22/??
SpecialProperties
TransitiveProperty
SymmetricProperty
FunctionalProperty
InverseFunctionalProperty
DepartmentofComputerScienceUniversityofSanFranciscop.23/??
BooleanCombinations
It'softenconvenienttoconstructnewclassesoutof
combinationsofoldclasses.
undergrads=fresh+sophs+juniors+seniors
students=undergrads+grads
TopStudents=studentsandhasGPA>3.5
DepartmentofComputerScienceUniversityofSanFranciscop.24/??
BooleanCombinations
<owl:Classrdf:about='students''>
<owl:unionOfrdf:parseType=''Collection''>
<owl:Classrdf:about=''#frosh''/>
<owl:Classrdf:about=''#soph''/>
<owl:Classrdf:about=''#junior''/>
<owl:Classrdf:about=''#senior''/>
</owl:unionOf>
</owl:Class>
DepartmentofComputerScienceUniversityofSanFranciscop.25/??
Uniquenames
OWLdoesnotadopttheuniquenamesassumption
typicallyseenindatabases.
Thesameobjectmighthavemorethanonename.
SupposeweassertthatCS680hasexactlyoneteacher,
thatBrooksteachesCS680,andthatChristeaches
CS680.
Databaseswouldcallthisaninconsistency
OWLreasonerswillconcludethatChris==Brooks
DepartmentofComputerScienceUniversityofSanFranciscop.26/??
Open-worldAssumption
AsinRDF,OWLusestheopenworldassumption.
Justbecausesomethingcannotbeshowntruedoesnot
meanitisfalse.
OWLDLisactuallyweakenoughthatthisisnottypically
aproblem;datacanstillbesharedwithDBswithout
problems.
DepartmentofComputerScienceUniversityofSanFranciscop.27/??
Inference
OWLOntologiescanthenbeloadedintoareasoner,
suchasPelletorRacer.
Thereasonerrunsinaforward-chainingmodeand
discoversallconsequencesoftheontology
Classicationofinstances,inconsistencies,
equivalentclasses.
Thismakesitpossibleforaknowledgeengineerto
incompletelydescribeadomain.
DepartmentofComputerScienceUniversityofSanFranciscop.28/??
Summary
OWLisanextremelypowerfulsetoflanguagesfor
modelingcomplex,richinformation
Sublanguagestradeexpressivenessfor
completeness
Requiressomeunderstandingoflogictouseproperly.
YoungestoftheSemanticWebtechnologies.
Currentlyinuseinbiomedical,bioinformaticsprojects.
DepartmentofComputerScienceUniversityofSanFranciscop.29/??