Introduction to OWL

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Introduction to OWL
2
Introduction

• RDF
• RDFS
• OWL Ontologies
• Sub-languages
• Conclusions

3
RDF - Resource Description Framework

• Directed Graph data model
• URI-based vocabulary
• XML format
• Fact assertion
• Entailment

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RDF Nodes

• 2 node types resources literals
• Statements (triples) consist of
• subject always a resource
• predicate always a resource
• object a resource or literal

urnaclRory
Rory Steele
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RDF Graph
urnaclRory
Rory Steele
urnaclFullName
urnacllocation
urnaclofficeG3a
urncrukHolborn
urncrukoffice
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RDF Schema

• A vocabulary for RDF statements
• Introduces classes and type
• Extends simple properties with notion of
  inheritance, domain and range
• Introduces containers Bags, Sequences, Alts and
  Lists
• Formalises reification of statements

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OWL

• Web Ontology Language
• Extends RDF Schema
• Makes an open world assumption
• Monotonic
• new entailments can only be added, never deleted
  (though they may be contradictory)
• Ontologies may consist of class declarations and
  instance data

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OWL Classes

• Named classes (via URI)
• Restricted classes
• Unions (logical disjunction)
• Intersections (logical conjunction)
• Enumerations
• Complement

9
Named Classes
ltowlClass rdfIDGrapegt lt/owlClassgt
ltowlClass rdfIDWineGrapegt
ltrdfssubClassOf rdfresourceGrape/gt
lt/owlClassgt
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Restricted Classes OWL Properties

• Object properties predicates from resources to
  resources
• Datatype properties predicates from resources
  to literals
• usually typed to some XML schema class (ex.
  xsdinteger)
• Use of domain and range on properties gives
  global constraints on a property

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Domain and Range
ltowlObjectProperty rdfID"madeFromGrape"gt
ltrdfsdomain rdfresource"Wine"/gt
ltrdfsrange rdfresource"WineGrape"/gt lt/owlObje
ctPropertygt
ltowlDatatypeProperty rdfID"yearValue"gt
ltrdfsdomain rdfresource"VintageYear" /gt
ltrdfsrange rdfresource"xsdpositiveInteger"/gt lt
/owlDatatypePropertygt
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Property Restrictions

• cardinality min, max and exact
• hasValue to specific instance
• allValuesFrom universal quantifier
• someValuesFrom existensial quantifier

ltowlClass rdfID"Wine"gt ltrdfssubClassOfgt
ltowlRestrictiongt ltowlonProperty
rdfresource"madeFromGrape"/gt
ltowlminCardinality rdfdatatypexsdnonNegativeI
nteger"gt1lt/owlminCardinalitygt
lt/owlRestrictiongt lt/rdfssubClassOfgt
... lt/owlClassgt
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Property Types

• subPropertyOf
• inverseOf
• functional
• transitive
• symmetric

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Intersections
WhiteWine is exactly the intersection of the
class Wine and the set of the things that have
the colour White
ltowlClass rdfIDWhiteWinegt
ltowlintersectionOf rdfparseTypeCollection/gt
ltowlClass rdfaboutWine/gt
ltowlRestrictiongt ltowlonProperty
rdfresourcehasColour/gt
ltowlhasValue rdfresourceWhite/gt
lt/owlRestrictiongt lt/owlintersectionOfgt lt/ow
lClassgt
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Unions
ltowlClass rdfIDWinegt ltowlunionOf
rdfparseTypeCollection/gt ltowlClass
rdfaboutWhiteWine/gt ltowlClass
rdfaboutRedWine/gt ltowlClass
rdfaboutRoseWine/gt ltowlClass
rdfaboutDessertWine/gt lt/owlunionOfgt lt/ow
lClassgt
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Enumerations
ltowlClass rdfID"WineColor"gt
ltrdfssubClassOf rdfresource"WineDescriptor"/gt
ltowloneOf rdfparseType"Collection"gt
ltWineColor rdfabout"White" /gt
ltWineColor rdfabout"Rose" /gt
ltWineColor rdfabout"Red" /gt
lt/owloneOfgt lt/owlClassgt
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Complement
ltowlClass rdfIDNonFrenchWinegt
ltowlintersectionOf rdfparseTypeCollection/gt
ltowlClass rdfaboutWine/gt
ltowlcomplementOfgt ltowlonProperty
rdfresourcelocation/gt
ltowlhasValue rdfresourceFrance/gt
lt/owl complementOfgt lt/owlintersectionOfgt lt/
owlClassgt
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Disjoint Classes
ltowlClass rdfID"Pasta"gt ltrdfssubClassOf
rdfresource"EdibleThing"/gt
ltowldisjointWith rdfresource"Meat"/gt
ltowldisjointWith rdfresource"Fowl"/gt
ltowldisjointWith rdfresource"Seafood"/gt
ltowldisjointWith rdfresource"Dessert"/gt
ltowldisjointWith rdfresource"Fruit"/gt lt/owlCl
assgt
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Individuals

• Resources that have a type of an OWL Class
• Individuals may have several types
• Individuals may be declared as semantically
  identical/different with the properties
  owlsameAs/owldifferentFrom

ltWine rdfIDRorysFavoriteCurry"gt
ltowlsameAs rdfresource"MeatJalfrezi"/gt lt/Winegt

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OWL Sub Languages

• OWL Lite
• Class hierarchies and simple restrictions
• OWL DL (Description Logics)
• Above with extra features whilst ensuring
  computational completeness and decidability
• OWL Full
• Above but with no computational guarantees (ex.
  Classes can also be Individuals)

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Conclusions

• Powerful ontology framework
• Formal semantics
• Open standard
• Integration with XML Schema for data primitives
• Growing number of public ontologies
• NCI Ontology
• Galen Anatomy
• Open EHR

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Future and Integration

• Tool support
• PROforma integration
• Authoring time
• Expression evaluation
• Query support
• RDQL
• XQuery

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