Dr. Alexandra I. Cristea

1
OWL

• Dr. Alexandra I. Cristea
• http//www.dcs.warwick.ac.uk/acristea/

2
What is OWL?

• OWL became a W3C (World Wide Web Consortium)
  Recommendation in February 2004.
• OWL stands for Web Ontology Language
• OWL is built on top of RDF
• OWL is for processing information on the web
• OWL was designed to be interpreted by computers
• OWL was not designed for being read by people
• OWL is written in XML
• OWL is a web standard
• OWL has three sublanguages

3
What is an Ontology?

• Ontology is about the exact description of things
  and their relationships and an inference
  mechanism for it.
• For the web, ontology is about the exact
  description of web information and relationships
  between web information and reasoning with it.
• dictionary ? taxonomy ? ontology

4
Ontology Origins and History
Ontology in Philosophy

• a philosophical disciplinea branch of
  philosophy that
• deals with the nature and the organisation of
  reality
• Science of Being (Aristotle, Metaphysics, IV, 1)
• Tries to answer the questions
• What characterizes being?
• Eventually, what is being?

5
Ontology in Linguistics
Tank
6
Ontology in Computer Science

• An ontology is an engineering artifact
• It is constituted by a specific vocabulary used
  to describe a certain reality, plus
• a set of explicit assumptions regarding the
  intended meaning of the vocabulary.
• Thus, an ontology describes a formal
  specification of a certain domain
• Shared understanding of a domain of interest
• Formal and machine manipulable model of a domain
  of interest

7
Why OWL?

• OWL is a part of the "Semantic Web Vision" - a
  future where
• Web information has exact meaning
• Web information can be processed by computers
• Computers can integrate information from the web

8
OWL was designed for Processing Information

• OWL was designed to provide a common way to
  process the content of web information (instead
  of displaying it).
• OWL was designed to be read by computer
  applications (instead of humans).

9
OWL is Different from RDF

• OWL , RDF similar
• but OWL
• stronger language
• greater machine interpretability
• larger vocabulary
• stronger syntax.

10
OWL Sublanguages

• OWL has three sublanguages
• OWL Lite
• hierarchy simple constraints cardinality
  0,1
• OWL DL (includes OWL Lite)
• complete, decidable (part of FOL)
• Type separations (class ltgt property ltgt
  individual)
• OWL Full (includes OWL DL)
• aug. meaning RDF..

11
OWL is Written in XML

• By using XML, OWL information can easily be
  exchanged between different types of computers
  using different types of operating system and
  application languages.
• Oh yes, there is a namespace
• xmlnsowl "http//www.w3.org/2002/07/owl"

12
(more on) OWL

• Based on predecessors (DAMLOIL)
• A Web Language Based on RDF(S)
• An Ontology Language Based on logic

13
OWL Ontologies

• Whats inside an OWL ontology
• Classes class-hierarchy
• Properties (Slots) / values
• Relations between classes(inheritance,
  disjoints, equivalents)
• Restrictions on properties (type, cardinality)
• Characteristics of properties (transitive, )
• Annotations
• Individuals
• Reasoning tasks classification, consistency
  checking

14
OWL Use Cases

• At least two different user groups
• OWL used as data exchange language(define
  interfaces of services and agents)
• OWL used for terminologies or knowledge models
• OWL DL is the subset of OWL (Full) that is
  optimized for reasoning and knowledge modeling

15
OWL Example (Airport)

• Example http//www.cs.man.ac.uk/rector/Modules/C
  S646-2004/Labs/Thursday/Simple_University-01.owl
• Find the error in the OWL Resource
  http//www.daml.org/2001/10/html/airport-ont
• Validators are
• For RDF http//www.w3.org/RDF/Validator
• For OWL http//phoebus.cs.man.ac.uk9999/OWL/Vali
  dator
• For a tutorial on XML, RDF, SPARQL, OWL see
  http//jmvidal.cse.sc.edu/talks/xmlrdfdaml/index.x
  ml?styleWhite
• Semantic web search engine http//swoogle.umbc.ed
  u/

16
Scenario

• Semantic Web for Tourism/Traveling
• Goal Find matching holiday destinations for a
  customer

I am looking for a comfortable destination with
beach access
Tourism Web
17
Scenario Architecture

• A search problem Match customers expectations
  with potential destinations
• Required Web Service that exploits formal
  information about the available destinations
• Accommodation (Hotels, BB, Camping, ...)
• Activities (Sightseeing, Sports, ...)

18
Tourism Semantic Web

• Open World
• New hotels are being added
• New activities are offered
• Providers publish their services dynamically
• Standard format / grounding is needed ?
  Tourism Ontology

19
Tourism Semantic Web
OWL Metadata (Individuals)
OWL Metadata (Individuals)
Tourism Ontology
Destination
Accomodation
Activity
OWL Metadata (Individuals)
OWL Metadata (Individuals)
Web Services
20
OWL

• Individuals (e.g., FourSeasons)
• Properties
• ObjectProperties (references)
• DatatypeProperties (simple values)
• Classes (e.g., Hotel)

21
Individuals (Instances)

• Represent objects in the domain
• Specific things
• Two names could represent the same real-world
  individual

22
Example of Individuals

• ltRegion rdfID"CentralCoastRegion" /gt
• equivalent to
• ltowlThing rdfID"CentralCoastRegion" /gt
• ltowlThing rdfabout"CentralCoastRegion"gt
  ltrdftype rdfresource"Region"/gt
• lt/owlThinggt

23
ObjectProperties

• Link two individuals together
• Relationships (0..n, n..m)

24
Example Property

• ltowlObjectProperty rdfID"course"gt ltrdfsdomain
  rdfresource"Meal" /gt ltrdfsrange
  rdfresource"MealCourse" /gt
• lt/owlObjectPropertygt

25
Property Domain Range

• If a relation issubject_individual ?
  hasProperty ? object_individual
• The domain is the class of the subject individual
• The range is the class of the object individual
  (or a datatype if hasProperty is a Datatype
  Property)

26
Properties, Range and Domain

• Property characteristics
• Domain left side of relation (Destination)
• Range right side (Accomodation)

27
Example Propery, Domain Range

• ltowlObjectProperty rdfID"madeFromGrape"gt
• ltrdfsdomain rdfresource"Wine"/gt
• ltrdfsrange rdfresource"WineGrape"/gt
• lt/owlObjectPropertygt
• ltowlObjectProperty rdfID"course"gt ltrdfsdomain
  rdfresource"Meal" /gt ltrdfsrange
  rdfresource"MealCourse" /gt
• lt/owlObjectPropertygt

28
Domains

• Individuals can only take values of properties
  that have matching domain
• Only Destinations can have Accommodations
• Domain can contain multiple classes
• Domain can be undefinedProperty can be used
  everywhere

29
Property Restriction Example Cardinality

• ltowlClass rdfID"Wine"gt
• ltrdfssubClassOf rdfresource"foodPotableLiq
  uid"/gt ltrdfssubClassOfgt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"madeFromGrape
  "/gt
• ltowlminCardinality rdfdatatype"xsdnonNeg
  ativeInteger"gt1lt/owlminCardinalitygt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt ...
• lt/owlClassgt

ltowlRestrictiongt ltowlonProperty
rdfresource"madeFromGrape"/gt
ltowlminCardinality rdfdatatype"xsdnonNegative
Integer"gt1lt/owlminCardinalitygt
lt/owlRestrictiongt
30
OWL Extends Other Ontologies

• extend existing ontology by saying things about
  terms in it
• ltowlClass rdfabout"Animal"gt
• ltrdfscommentgt
• Animals have exactly two parents, ie If x is
  an animal, it has exactly 2 parents (but NOT
  anything that has 2 parents is an animal).
• lt/rdfscommentgt
• ltrdfssubClassOfgt
• ltowlRestriction owlcardinality"2"gt
• ltowlonProperty rdfresource"hasParent
  "/gt
• lt/owlRestrictiongt
• lt/rdfssubClassOfgt
• lt/owlClassgt
• If ontology is already published, you use the
  full URL.
• ltowlClass rdfabout"http//www.sample.com/ontolo
  gies/zooAnimal"gt

31
Inverse Properties

• Represent bidirectional relationships
• Adding a value to one property also adds a value
  to the inverse property (!)

32
Inverse Property Example

• ltowlObjectProperty rdfID"hasMaker"gt
• ltrdftype rdfresource"owlFunctionalProperty
  " /gt
• lt/owlObjectPropertygt
• ltowlObjectProperty rdfID"producesWine"gt
  ltowlinverseOf rdfresource"hasMaker" /gt
• lt/owlObjectPropertygt

33
Transitive Properties

• If A is related to B and B is related to C then A
  is also related to C
• Often used for part-of relationships

34
Transitive Property Example

• ltowlObjectProperty rdfID"locatedIn"gt
• ltrdftype rdfresource"owlTransitiveProperty"
  /gt
• ltrdfsdomain rdfresource"owlThing" /gt
• ltrdfsrange rdfresource"Region" /gt
• lt/owlObjectPropertygt
• ltRegion rdfID"SantaCruzMountainsRegion"gt
• ltlocatedIn rdfresource"CaliforniaRegion" /gt
• lt/Regiongt
• ltRegion rdfID"CaliforniaRegion"gt
• ltlocatedIn rdfresource"USRegion" /gt
• lt/Regiongt

35
Sub-properties Example

• ltowlObjectProperty rdfID"hasWineDescriptor"gt
  ltrdfsdomain rdfresource"Wine" /gt
• ltrdfsrange rdfresource"WineDescriptor" /gt
• lt/owlObjectPropertygt
• ltowlObjectProperty rdfID"hasColor"gt
  ltrdfssubPropertyOf rdfresource"hasWineDescript
  or" /gt
• ltrdfsrange rdfresource"WineColor" /gt ...
• lt/owlObjectPropertygt

36
DatatypeProperties

• Link individuals to primitive values(integers,
  floats, strings, booleans etc)
• Often AnnotationProperties without formal
  meaning

hasSize 4,500,000 isCapital true rdfscomment
Dont miss the opera house
37
Classes

• Sets of individuals with common characteristics
• Individuals are instances of at least one class

38
Examples of Classes in OWL

• ltowlClass rdfID"Winery"/gt
• ltowlClass rdfID"Region"/gt
• ltowlClass rdfID"ConsumableThing"/gt

39
Superclass Relationships

• Classes can be organized in a hierarchy
• Direct instances of subclass are also (indirect)
  instances of superclasses

40
Example Subclasses

• ltowlClass rdfID"PotableLiquid"gt
• ltrdfssubClassOf rdfresource"ConsumableThi
  ng" /gt
• lt/owlClassgt
• ltowlClass rdfID"Wine"gt
• ltrdfssubClassOf rdfresource"foodPotableLiqu
  id"/gt
• ltrdfslabel xmllang"en"gtwinelt/rdfslabelgt
• ltrdfslabel xmllang"fr"gtvinlt/rdfslabelgt ...
  
• lt/owlClassgt

41
Class Relationships

• Classes can overlap arbitrarily

42
Class Disjointness

• All classes could potentially overlap
• In many cases we want to make sure they dont
  share instances

disjointWith
43
Example disjoint

• ltowlClass rdfabout"Man"gt ltowldisjointWith
  rdfresource"Woman"/gt
• lt/owlClassgt

44
Class versus Individual (Instance)

• Levels of representation
• In certain contexts a class can be considered an
  instance of something else.
• Grape, set of all grape varietals.
  CabernetSauvingonGrape is an instance of this
  class, but could be considered a class, the set
  of all actual Cabernet Sauvignon grapes.
• Subclass vs. instance easy to confuse
  instance-of relationship with subclass
  relationship!
• CabernetSauvignonGrape as individual instance
  of Grape, or subclass of Grape.
• But Grape class is the set of all grape
  varietals, any subclass should be a subset.
• CabernetSauvignonGrape is an instance of Grape,
  It does not describe a subset of Grape varietals,
  it is a grape varietal.

45
Class Descriptions

• Classes can be described by their logical
  characteristics
• Descriptions are anonymous classes

46
Class Descriptions

• Define the meaning of classes
• Anonymous class expressions are used
• All national parks have campgrounds.
• A backpackers destination is a destination that
  has budget accommodation and offers sports or
  adventure activities.
• Expressions mostly restrict property values (OWL
  Restrictions)

47
Class Descriptions Why?

• Based on OWLs Description Logic support
• Formalize intentions and modeling decisions
  (comparable to test cases)
• Make sure that individuals fulfill conditions
• Tool-supported reasoning

48
Reasoning with Classes

• Tool support for 3 types of reasoning exists
• Consistency checkingCan a class have any
  instances?
• ClassificationIs A a subclass of B?
• Instance classificationWhich classes does an
  individual belong to?

49
Restrictions (Overview)

• Define a condition for property values
• allValuesFrom
• someValuesFrom
• hasValue
• minCardinality
• maxCardinality
• cardinality
• An anonymous class consisting of all individuals
  that fulfill the condition

50
Cardinality Restrictions

• Meaning The property must have at least/at
  most/exactly x values
• is the shortcut for and
• Example A FamilyDestination is a Destination
  that has at least one Accomodation and at least 2
  Activities

51
allValuesFrom Restrictions

• Meaning All values of the property must be of a
  certain type
• Warning Also individuals with no values fulfill
  this condition (trivial satisfaction)
• Example Hiking is a Sport that is only possible
  in NationalParks

52
Value constraints

• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasParent" /gt
  ltowlallValuesFrom rdfresource"Human" /gt
• lt/owlRestrictiongt

53
someValuesFrom Restrictions

• Meaning At least one value of the property must
  be of a certain type
• Others may exist as well
• Example A NationalPark is a RuralArea that has
  at least one Campground and offers at least one
  Hiking opportunity

54
hasValue Restrictions

• Meaning At least one of the values of the
  property is a certain value
• Similar to someValuesFrom but with
  Individuals and primitive values
• Example A PartOfSydney is a Destination where
  one of the values of the isPartOf property is
  Sydney

55
Enumerated Classes

• Consist of exactly the listed individuals

56
Example Description Enumeration

• ltowlClassgt
• ltowloneOf rdfparseType"Collection"gt
• ltowlThing rdfabout"Eurasia"/gt
• ltowlThing rdfabout"Africa"/gt
• ltowlThing rdfabout"NorthAmerica"/gt
• ltowlThing rdfabout"SouthAmerica"/gt
• ltowlThing rdfabout"Australia"/gt
• ltowlThing rdfabout"Antarctica"/gt
  lt/owloneOfgt
• lt/owlClassgt

57
Logical Class Definitions

• Define classes out of other classes
• unionOf (or)
• intersectionOf (and)
• complementOf (not)
• Allow arbitrary nesting of class descriptions (A
  and (B or C) and not D)

58
unionOf

• The class of individuals that belong to class A
  or class B (or both)
• Example Adventure or Sports activities

59
intersectionOf

• The class of individuals that belong to both
  class A and class B
• Example A BudgetHotelDestination is a
  destination with accomodation that is a budget
  accomodation and a hotel

60
Implicit intersectionOf

• When a class is defined by more than one class
  description, then it consists of the intersection
  of the descriptions
• Example A luxury hotel is a hotel that is also
  an accommodation with 3 stars

61
complementOf

• The class of all individuals that do not belong
  to a certain class
• Example A quiet destination is a destination
  that is not a family destination

62
Class Conditions

• Necessary Conditions(Primitive / partial
  classes)If we know that something is a X,then
  it must fulfill the conditions...
• Necessary Sufficient Conditions(Defined /
  complete classes)If something fulfills the
  conditions...,then it is an X.

63
Class Conditions (2)
(not everything that fulfills theseconditions is
a NationalPark)
(everything that fulfills theseconditions is a
QuietDestination)
64
Classification

• A RuralArea is a Destination
• A Campground is BudgetAccomodation
• Hiking is a Sport
• ThereforeEvery NationalPark is a
  Backpackers-Destination

(Other BackpackerDestinations)
65
Reasoning with Propery, Domain Range

• ltowlObjectProperty rdfID"madeFromGrape"gt
• ltrdfsdomain rdfresource"Wine"/gt
• ltrdfsrange rdfresource"WineGrape"/gt
• lt/owlObjectPropertygt
• ltowlThing rdfID"LindemansBin65Chardonnay"gt
  ltmadeFromGrape rdfresource"ChardonnayGrape" /gt
• lt/owlThinggt  

66
Visualization with OWLViz
67
Putting it All Together

• Ontology has been developed
• Published on a dedicated web address
• Ontology provides standard terminology
• Other ontologies can extend it
• Users can instantiate the ontology to provide
  instances
• specific hotels
• specific activities

68
Ontology Import

• Adds all classes, properties and individuals from
  an external OWL ontology into your project
• Allows to create individuals, subclasses, or to
  further restrict imported classes
• Can be used to instantiate an ontology for the
  Semantic Web

69
Tourism Semantic Web (2)
OWL Metadata (Individuals)
Tourism Ontology
Destination
Accommodation
Activity
Web Services
70
OWL File
lt?xml version"1.0"?gt ltrdfRDF
xmlnsrdf"http//www.w3.org/1999/02/22-rdf-syntax
-ns" xmlnsrdfs"http//www.w3.org/2000/01/rd
f-schema" xmlnsowl"http//www.w3.org/2002/0
7/owl" xmlnsdc"http//purl.org/dc/elements/
1.1/" xmlnstravel"http//protege
.stanford.edu/plugins/ owl/owl-library/travel.o
wl" xmlbase"http//protege.stanford.edu/plugi
ns/owl/owl- library/heli-bunjee.owl"gt . .
. lt/rdfRDFgt
71
OWL File . . . OWL body in RDF wrap
ltowlOntology rdfabout""gt ltowlimports
rdfresource"http//protege.stanford.edu/
plugins/owl/owl-library/travel.owl"/gt
lt/owlOntologygt ltowlClass rdfID"HeliBunjeeJu
mping"gt ltrdfssubClassOf rdfresource"http//
protege.stanford. edu/plugins/owl/owl-library/
travel.owlBunjeeJumping"/gt lt/owlClassgt
ltHeliBunjeeJumping rdfID"ManicSuperBunjee"gt
lt/HeliBunjeeJumpinggt
72
OWL File in HeliBunjeeJumping
lttravelisPossibleIngt ltrdfDescription
rdfabout"http//protege.stanford.edu/plugins/owl
/owl- library/travel.owlSydney"gt
lttravelhasActivity rdfresource"ManicSuperBunje
e"/gt lt/rdfDescriptiongt
lt/travelisPossibleIngt lttravelhasContactgt
lt/travelhasContactgt
ltrdfscomment rdfdatatype"http//www.w3.org/2001
/XMLSchemastring"gtManic super bunjee now offers
nerve wrecking jumps from 300 feet right out of
a helicopter. Satisfaction guaranteed.lt/rdfscomm
entgt
73
OWL File in travelhasContact
lttravelContact rdfID"MSBInc"gt
lttravelhasEmail rdfdatatype"http//www.w3.org/2
001/XMLSchemastring"gtmsb_at_manicsuperbunjee.com
lt/travelhasEmailgt lttravelhasCity
rdfdatatype"http//www.w3.org/2001/XMLSchemastr
ing"gtSydneylt/travelhasCitygt
lttravelhasStreet rdfdatatype"http//www.w3.org/
2001/XMLSchemastring"gtQueen Victoria
Stlt/travelhasStreetgt lttravelhasZipCode
rdfdatatype"http//www.w3.org/2001/XMLSchemaint
"gt1240lt/travelhasZipCodegt lt/travelContactgt
74
OWL Lite Synopsis

• Header Information
• Ontology
• imports
• Class Intersection
• intersectionOf
• Versioning
• versionInfo
• priorVersion
• backwardCompatibleWith
• incompatibleWith
• DeprecatedClass
• DeprecatedProperty
• Annotation Properties
• rdfslabel
• rdfscomment
• rdfsseeAlso
• rdfsisDefinedBy
• AnnotationProperty
• OntologyProperty

• Property Characteristics
• ObjectProperty
• DatatypeProperty
• inverseOf
• TransitiveProperty
• SymmetricProperty
• FunctionalProperty
• InverseFunctionalProperty
• Property Restrictions
• Restriction
• onProperty
• allValuesFrom
• someValuesFrom
• Restricted Cardinality
• minCardinality (only 0 or 1)
• maxCardinality (only 0 or 1)
• cardinality (only 0 or 1)

• RDF Schema Features
• Class (Thing, Nothing)
• rdfssubClassOf
• rdfProperty
• rdfssubPropertyOf
• rdfsdomain
• rdfsrange
• Individual
• (In)Equality
• equivalentClass
• equivalentProperty
• sameAs
• differentFrom
• AllDifferent
• distinctMembers

75
OWL DL Full

• Class Axioms
• oneOf, dataRange
• disjointWith
• equivalentClass(applied to class expressions)
• rdfssubClassOf(applied to class expressions)
• Boolean Combinations of Class Expressions
• unionOf
• complementOf
• intersectionOf
• Arbitrary Cardinality
• minCardinality
• maxCardinality
• cardinality
• Filler Information
• hasValue

76
Problems with RDFS

• RDFS too weak to describe resources in sufficient
  detail
• No localised range and domain constraints
• Cant say that the range of hasChild is person
  when applied to persons and elephant when applied
  to elephants
• No existence/cardinality constraints
• Cant say that all instances of person have a
  mother that is also a person, or that persons
  have exactly 2 parents
• No transitive, inverse or symmetrical properties
• Cant say that isPartOf is a transitive property,
  that hasPart is the inverse of isPartOf or that
  touches is symmetrical
• Difficult to provide reasoning support
• No native reasoners for non-standard semantics
• May be possible to reason via FO axiomatisation

77
Web Ontology Language Requirements

• Desirable features identified for Web Ontology
  Language
• Extends existing Web standards
• Such as XML, RDF, RDFS
• Easy to understand and use
• Should be based on familiar KR idioms
• Formally specified
• Of adequate expressive power
• Possible to provide automated reasoning support

78
From RDF to OWL

• Two languages developed to satisfy above
  requirements
• OIL developed by group of (largely) European
  researchers (several from EU OntoKnowledge
  project)
• DAML-ONT developed by group of (largely) US
  researchers (in DARPA DAML programme)
• Efforts merged to produce DAMLOIL
• Development was carried out by Joint EU/US
  Committee on Agent Markup Languages
• Extends (DL subset of) RDF
• DAMLOIL submitted to W3C as basis for
  standardisation
• Web-Ontology (WebOnt) Working Group formed
• WebOnt group developed OWL language based on
  DAMLOIL
• OWL language now a W3C Proposed Recommendation

79
OWL Language

• Three species of OWL
• OWL full is union of OWL syntax and RDF
• OWL DL restricted to FOL fragment (¼ DAMLOIL)
• OWL Lite is easier to implement subset of OWL
  DL
• Semantic layering
• OWL DL ¼ OWL full within DL fragment
• DL semantics officially definitive
• OWL DL based on SHIQ Description Logic
• In fact it is equivalent to SHOIN(Dn) DL
• OWL DL Benefits from many years of DL research
• Well defined semantics
• Formal properties well understood (complexity,
  decidability)
• Known reasoning algorithms
• Implemented systems (highly optimised)

80
OWL built-in classes

• owlFunctionalProperty, owlInverseFunctionalPrope
  rty, owlSymmetricProperty, owlTransitiveProperty
  , owlDeprecatedClass, owlDeprecatedProperty

81
OWL built in properties

• owlequivalentClass, owldisjointWith,
  owlequivalentProperty, owlinverseOf,
  owlsameAs, owldifferentFrom, owlcomplementOf,
  owlunionOf, owlintersectionOf, owloneOf,
  owlallValuesFrom, owlonProperty,
  owlsomeValuesFrom, owlhasValue,
  owlminCardinality, owlmaxCardinality,
  owlcardinality, owldistinctMembers
• annotation properties owlversionInfo,
  rdfslabel, rdfscomment, rdfsseeAlso,
  rdfsisDefinedBy
• ontology properties owlimports,
  owlpriorVersion, owlbackwardCompatibleWith,
  owlincompatibleWith

82
OWL Class Constructors

• XMLS datatypes as well as classes in
• Arbitrarily complex nesting of constructors

83
OWL Syntax
E.g., Person hasChild.Doctor hasChild.Doctor

• ltowlClassgt
• ltowlintersectionOf rdfparseType"
  collection"gt
• ltowlClass rdfabout"Person"/gt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasChild"/gt
• ltowltoClassgt
• ltowlunionOf rdfparseType" collection"gt
• ltowlClass rdfabout"Doctor"/gt
• ltowlRestrictiongt
• ltowlonProperty rdfresource"hasChil
  d"/gt
• ltowlhasClass rdfresource"Doctor"/gt
  
• lt/owlRestrictiongt
• lt/owlunionOfgt
• lt/owltoClassgt
• lt/owlRestrictiongt
• lt/owlintersectionOfgt
• lt/owlClassgt

84
OWL Axioms
85
XML Schema Datatypes in OWL

• OWL supports XML Schema primitive datatypes
• E.g., integer, real, string,
• Strict separation between object classes and
  datatypes
• Disjoint interpretation domain for datatypes
• Disjoint object and datatype properties

86
Why Separate Classes and Datatypes?

• Philosophical reasons
• Datatypes structured by built-in predicates
• Not appropriate to form new datatypes using
  ontology language
• Practical reasons
• Ontology language remains simple and compact
• Semantic integrity of ontology language not
  compromised
• Implementability not compromised can use hybrid
  reasoner

87
OWL query language OWL-QL

• OWL Query Language (OWL-QL) is an updated version
  of the DAML Query Language (DQL).
• It is intended to be a candidate standard
  language and protocol for query-answering
  dialogues among Semantic Web computational
  agents.

88
OWL Conclusion

• We have learned
• OWL definition
• OWL comparison with RDF
• OWL classes and properties
• Usage scenarios