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OWL: The Web Ontology Language. Semantic Web Lecture Lecture VII – xx 2009 Dieter Fensel. Slides by: Federico M. Facca. Where are we?. Overview. Introduction and Motivation Technical Solution Design of OWL OWL Layering OWL and Description Logics OWL Syntaxes

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owl the web ontology language

OWL: The Web Ontology Language

Semantic Web Lecture Lecture VII – xx 2009

Dieter Fensel

Slides by: Federico M. Facca

overview
Overview
  • Introduction and Motivation
  • Technical Solution
    • Design of OWL
    • OWL Layering
    • OWL and Description Logics
    • OWL Syntaxes
  • Illustration by a large example
  • Extensions
overview1
Overview
  • Limitations of RDFS
    • Expressivity limitations
    • Layering Problems
  • Web Ontology Language OWL
    • Design of OWL
    • OWL Layering
    • OWL and Description Logics
    • OWL Syntaxes
what we discussed so far
What we discussed so far…
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
what we discussed so far1
What we discussed so far…
  • RDF Vocabulary
  • Classes:
    • rdf:Property, rdf:Statement, rdf:XMLLiteral
    • rdf:Seq, rdf:Bag, rdf:Alt, rdf:List
  • Properties:
    • rdf:type, rdf:subject, rdf:predicate, rdf:object,
    • rdf:first, rdf:rest, rdf:_n
    • rdf:value
  • Resources:
    • rdf:nil
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
what we discussed so far2
What we discussed so far…
  • RDF Vocabulary
  • Classes:
    • rdf:Property, rdf:Statement, rdf:XMLLiteral
    • rdf:Seq, rdf:Bag, rdf:Alt, rdf:List
  • Properties:
    • rdf:type, rdf:subject, rdf:predicate, rdf:object,
    • rdf:first, rdf:rest, rdf:_n
    • rdf:value
  • Resources:
    • rdf:nil
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
  • RDFS Vocabulary
  • RDFS Properties
    • rdfs:domain
    • rdfs:range
    • rdfs:subPropertyOf
    • rdfs:subClassOf
    • rdfs:member
    • rdfs:seeAlso
    • rdfs:isDefinedBy
    • rdfs:comment
    • rdfs:label
  • RDFS Vocabulary
  • RDFS Classes
    • rdfs:Resource
    • rdfs:Class
    • rdfs:Literal
    • rdfs:Datatype
    • rdfs:Container
    • rdfs:ContainerMembershipProperty
what we discussed so far3
What we discussed so far…
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
what we discussed so far4
What we discussed so far…
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
what we discussed so far5
What we discussed so far…
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer
what we discussed so far6
What we discussed so far…
  • RDF Schema
    • RDFS Vocabulary
    • RDFS Metadata
    • Literals and Datatypes in RDFS
  • Semantics of RDF and RDF Schema
    • Semantic notions
    • RDF(S) Entailment
  • SPARQL
    • SPARQL Queries
    • Query Answer

PREFIX vCard: <http://www.w3.org/2001/vcard-rdf/3.0#>

SELECT ?fullName

WHERE {?x vCard:FN ?fullName}

requirements for ontology languages
Requirements for Ontology Languages
  • Well-defined syntax
  • Convenience of expression
  • Formal semantics
    • Needed in reasoning, e.g.:
      • Class membership
      • Equivalence of classes
      • Consistency
      • Classification
  • Efficient reasoning support
  • Sufficient expressive power
limitations of rdfs
Limitations of RDFS
  • No semantics for:
    • Containers
    • Collections
    • Reification
  • Domain and range of property infer information rather than check data
    • Conjunctive interpretation of multiple restrictions
  • Use of properties as objects
  • RDF/XML syntax very verbose
rdfs as an ontology language
RDFS as an Ontology Language
  • Classes
  • Properties
  • Class hierarchies
  • Property hierarchies
  • Domain and range restrictions
expressiveness limitations of rdf s
Expressiveness limitations of RDF(S)
  • Only binary relations
  • Characteristics of Properties
    • e.g. inverse, transitive, symmetric
  • Local range restrictions
    • e.g. for class Person, the property hasName has range xsd:string
  • Complex concept descriptions
    • e.g. Person is defined by Man and Woman
  • Cardinality restrictions
    • e.g. a Person may have at most 1 name
  • Disjointness axioms
    • e.g. nobody can be both a Man and a Woman
layering issues
Layering issues
  • Syntax
    • Only binary relations in RDF
    • Verbose Syntax
    • No limitations on graph in RDF
      • Every graph is valid
  • Semantics
    • Malformed graphs
    • Use of vocabulary in language
      • e.g. <rdfs:Class, rdfs:subClassOf, ex:a>
    • Meta-classes
      • e.g. <ex:a, rdf:type, ex:a>
stack of languages
Stack of Languages
  • XML
    • Surface syntax, no semantics
  • XML Schema
    • Describes structure of XML documents
  • RDF
    • Datamodel for “relations” between “things”
  • RDF Schema
    • RDF Vocabulary Definition Language
  • OWL
    • A more expressive Vocabulary Definition Language

This and following slides in part due to Frank van Harmelen http://www.cs.vu.nl/~frankh/spool/SemWebSlides/OWL.ppt

rdf schema recap
RDF Schema Recap
  • RDFS provides
    • Classes
    • Class hierarchies
    • Properties
    • Property hierarchies
    • Domain and range restrictions
  • RDFS does not provide
    • Property characteristics (inverse, transitive, ...)
    • Local range restrictions
    • Complex concept definitions
    • Cardinality restrictions
    • Disjointness axioms
extending rdf schema
Extending RDF Schema
  • OWL extends RDF Schema to a full-fledged knowledge representation language for the Web
    • logical expressions (and, or, not)
    • (in)equality
    • local properties
    • required/optional properties
    • required values
    • enumerated classes
    • symmetry, inverse
design goals for owl
Design Goals for OWL
  • Shareable
  • Changing over time
  • Interoperability
  • Inconsistency detection
  • Balancing expressivity and complexity
  • Ease of use
  • Compatible with existing standards
  • Internationalization
requirements for owl
Requirements for OWL
  • Ontologies are object on the Web
  • with their own meta-data, versioning, etc...
  • Ontologies are extendable

From Grigoris Antoniou and Frank van Harmelen: A Semantic Web Primer, MIT Press 2004

requirements for owl1
Requirements for OWL
  • Ontologies are object on the Web
  • with their own meta-data, versioning, etc...
  • Ontologies are extendable
  • They contain classes, properties, data-types, range/domain, individuals
  • Equality (for classes, for individuals)
  • Classes as instances
  • Cardinality constraints
  • XML syntax
objectives for owl
Objectives for OWL

Objectives:

  • layered language
  • complex datatypes
  • digital signatures
  • decidability (in part)
  • local unique names (in part)

Disregarded:

  • default values
  • closed world option
  • property chaining
  • arithmetic
  • string operations
  • partial imports
  • view definitions
  • procedural attachments

A logical system or theory is decidable if there exists an

effective method such that for every formula in the system

the method is capable of deciding whether the formula is valid

in the system or not.

[http://www.wikipedia.org]

language layers of owl
Language Layers of OWL
  • OWL Lite
    • Classification hierarchy
    • Simple constraints
  • OWL DL
    • Maximal expressiveness while maintaining tractability
    • Standard formalization in a DL
  • OWL Full
    • Very high expressiveness
    • Losing tractability
    • All syntactic freedom of RDF (self-modifying)
language layers of owl1
Language Layers of OWL

Problems that are solvable in theory

but cannot be solved in practice are called intractable.

[http://www.wikipedia.org]

  • OWL Lite
    • Classification hierarchy
    • Simple constraints
  • OWL DL
    • Maximal expressiveness while maintaining tractability
    • Standard formalization in a DL
  • OWL Full
    • Very high expressiveness
    • Losing tractability
    • All syntactic freedom of RDF (self-modifying)
features of owl language layers
Features of OWL language layers
  • OWL Lite
    • (sub)classes, individuals
    • (sub)properties, domain, range
    • conjunction
    • (in)equality
    • cardinality 0/1
    • datatypes
    • inverse, transitive, symmetric properties
    • someValuesFrom
    • allValuesFrom
  • OWL DL
    • Negation
    • Disjunction
    • Full cardinality
    • Enumerated types
    • hasValue
  • OWL Full
    • Meta-classes
    • Modify language
owl full
OWL Full
  • No restriction on use of vocabulary (as long as legal RDF)
    • Classes as instances (and much more)
  • RDF style model theory
    • Reasoning using FOL engine
    • Semantics should correspond to OWL DL for restricted KBs
owl dl
OWL DL
  • Use of vocabulary restricted
    • Can’t be used to do “nasty things” (e.g. modify OWL)
    • No classes as instances
    • Defined by abstract syntax
  • Standard DL-based model theory
    • Direct correspondence with a DL
    • Partial reasoning via DL engines
    • Reasoning for full language via FOL engines
      • No need for axiomatization
      • Built-in datatypes required for performance
owl lite
OWL Lite
  • No explicit negation or union
  • Restricted cardinality (0/1)
  • No nominals (oneOf)
  • DL-based semantics
    • Reasoning via DL engines (+ datatypes)
  • Semantically, only small restriction on OWL DL
    • No nominals
    • No arbitrary cardinality
owl and description logics
OWL and Description Logics
  • OWL Lite corresponds to the DL SHIN(D)
    • Named classes (A)
    • Named properties (P)
    • Individuals (C(o))
    • Property values (P(o, a))
    • Intersection (C ⊓ D)
    • Union(!) (C ⊔ D)
    • Negation(!) (¬C)
    • Existential value restrictions (∃P.C)
    • Universal value restrictions (∀P.C)
    • Unqualified number restrictions (≥ nP, ≤ nP, = nP)
  • OWL DL corresponds to the DL SHOIN(D)
    • Property value (∃ P.{o})
    • Enumeration ({o1, ..., on})
owl constructs
OWL constructs

+ XML Schema datatypes: int, string, real, etc...

more on owl species
More on OWL species
  • OWL Full is not a Description Logic
  • OWL Lite has strong syntactic restrictions, but only limites semantics restrictions, compared with OWL DL
    • Negation can be encoded using disjointness
    • With negation and conjunction, you can encode disjunction

Class(C complete unionOf(B C))

is equivalent to:

DisjointClasses(notB B)

DisjointClasses(notC C)

Class(notBandnotC complete notB notC)

DisjointClasses(notBandnotC BorC)

Class(C complete notBandnotC)

more on layering
More on layering
  • For an OWL DL-restricted KB, OWL Full semantics is not equivalent to OWL DL semantics

John friend Susan

OWL Full entails:

John rdf:type owl:Thing

Susan rdf:type owl:Thing

friend rdf:type owl:ObjectProperty

John rdf:type _:x

_:x owl:onProperty friend

_:x owl: minCardinality ”1”ˆˆxsd:nonNegativeInteger

syntaxes of owl
Syntaxes of OWL
  • RDF
    • Official exchange syntax
    • Hard for humans
    • RDF parsers are hard to write!
  • UML
    • Large user base
  • XML
    • Not the RDF syntax
    • Better for humans
    • More XML than RDF tools available
  • Abstract syntax
    • Not defined for OWL Full
    • Human readable
owl in rdf xml
OWL in RDF/XML

Example from [OwlGuide]:

<!ENTITY vin ”http://www.w3.org/TR/2004/REC−owl−guide−20040210/wine#” >

<!ENTITY food ”http://www.w3.org/TR/2004/REC−owl−guide−20040210/food#” >

...

<rdf:RDF xmlns:vin=”http://www.w3.org/TR/2004/REC−owl−guide−20040210/wine#”

xmlns:food=”http://www.w3.org/TR/2004/REC−owl−guide−20040210/food#”

... >

<owl:Class rdf:ID=”Wine”>

<rdfs:subClassOf rdf:resource=”&food;PotableLiquid”/>

<rdfs:label xml:lang=”en”>wine</rdfs:label>

<rdfs:label xml:lang=”fr”>vin</rdfs:label>

...

</owl:Class>

<owl:Class rdf:ID=”Pasta”>

<rdfs:subClassOf rdf:resource=”#EdibleThing” />

...

</owl:Class>

</rdf:RDF>

owl in rdf xml1
OWL in RDF/XML

Example from [OwlGuide]:

<!ENTITY vin ”http://www.w3.org/TR/2004/REC−owl−guide−20040210/wine#” >

<!ENTITY food ”http://www.w3.org/TR/2004/REC−owl−guide−20040210/food#” >

...

<rdf:RDF xmlns:vin=”http://www.w3.org/TR/2004/REC−owl−guide−20040210/wine#”

xmlns:food=”http://www.w3.org/TR/2004/REC−owl−guide−20040210/food#”

... >

<owl:Class rdf:ID=”Wine”>

<rdfs:subClassOf rdf:resource=”&food;PotableLiquid”/>

<rdfs:label xml:lang=”en”>wine</rdfs:label>

<rdfs:label xml:lang=”fr”>vin</rdfs:label>

...

</owl:Class>

<owl:Class rdf:ID=”Pasta”>

<rdfs:subClassOf rdf:resource=”#EdibleThing” />

...

</owl:Class>

</rdf:RDF>

From Grigoris Antoniou and Frank van Harmelen: A Semantic Web Primer, MIT Press 2004

owl abstract syntax
OWL Abstract syntax

Class(professor partial )

Class(associateProfessor partial academicStaffMember)

DisjointClasses(associateProfessorassistantProfessor)

DisjointClasses(professorassociateProfessor)

Class(faculty complete academicStaffMember)

owl abstract syntax1
OWL Abstract syntax
  • In DL syntax:

associateProfessor ⊑ academicStaffMember

associateProfessor ⊑ ¬assistantProfessor

professor ⊑ ¬associateProfessor

faculty ≡ academicStaffMember

Class(professor partial )

Class(associateProfessor partial academicStaffMember)

DisjointClasses(associateProfessor assistantProfessor)

DisjointClasses(professor associateProfessor)

Class(faculty complete academicStaffMember)

more examples
More Examples

DatatypeProperty(age range(xsd:nonNegativeInteger))

ObjectProperty(lecturesIn)

ObjectProperty(isTaughtBy domain(course) range(academicStaffMember))

SubPropertyOf(isTaughtByinvolves)

ObjectProperty(teaches inverseOf(isTaughtBy)

domain(academicStaffMember)

range(course))

EquivalentProperties(lecturesInteaches)

ObjectProperty(hasSameGradeAsTransitive Symmetric

domain(student)

range(student))

more examples1
More Examples

DatatypeProperty(age

range(xsd:nonNegativeInteger))

ObjectProperty(lecturesIn)

ObjectProperty(isTaughtBy

domain(course)

range(academicStaffMember))

SubPropertyOf(isTaughtBy involves)

ObjectProperty(teaches

inverseOf(isTaughtBy)

domain(academicStaffMember)

range(course))

EquivalentProperties(lecturesIn teaches)

ObjectProperty(hasSameGradeAs

Transitive Symmetric

domain(student)

range(student))

  • In DL syntax:

⊤⊑∀age.xsd:nonNegativeInteger

⊤⊑∀isTaughtBy−.course

⊤⊑∀isTaughtBy.academicStaffMember

isTaughtBy ⊑ involves

teaches ≡ isTaughtBy−

⊤⊑∀teaches−.academicStaffMember

⊤⊑∀teaches.course

lecturesIn ≡ teaches

hasSameGradeAs+⊑ hasSameGradeAs

hasSameGradeAs ≡ hasSameGradeAs−

⊤⊑∀hasSameGradeAs−.student

⊤⊑∀hasSameGradeAs.student

more examples2
More Examples

Individual(949318 type(lecturer))

Individual(949352type(academicStaffMember)

value(age ”39”ˆˆ&xsd;integer))

ObjectProperty(isTaughtBy Functional)

Individual(CIT1111type(course)

value(isTaughtBy 949352)

value(isTaughtBy 949318))

DifferentIndividuals(949318 949352)

DifferentIndividuals(949352 949111 949318)

more examples3
More Examples
  • In DL syntax:

949318 : lecturer

949352 : academicStaffMember

949352, ”39”ˆˆ&xsd; integer:age

⊤⊑≤1isTaughtBy

CIT1111 : course

CIT1111, 949352:isTaughtBy

CIT1111, 949318:isTaughtBy

949318 ≠ 949352

949352 ≠ 949111

949111 ≠ 949318

949352≠ 949318

Individual(949318 type(lecturer))

Individual(949352

type(academicStaffMember)

value(age ”39”ˆˆ&xsd;integer))

ObjectProperty(isTaughtBy Functional)

Individual(CIT1111 type(course)

value(isTaughtBy 949352)

value(isTaughtBy 949318))

DifferentIndividuals(949318 949352)

DifferentIndividuals(949352 949111 949318)

more examples4
More Examples

Class(firstYearCourse partial

restriction(isTaughtBy allValuesFrom (Professor)))

Class(mathCourse partial

restriction(isTaughtBy hasValue (949352)))

Class(academicStaffMember partial

restriction (teaches someValuesFrom (undergraduateCourse)))

Class(course partial

restriction (isTaughtBy minCardinality (1)))

Class(department partial

restriction (hasMember minCardinality(10))

restriction (hasMember maxCardinality(30)))

more examples5
More Examples
  • In DL syntax:

firstYearCourse ⊑ ∀isTaughtBy.Professor

mathCourse ⊑∃isTaughtBy.{949352}

academicStaffMember ⊑∃teaches.undergraduateCourse

course ⊑ ≥1isTaughtBy

department ⊑≥10hasMember ⊓≤30hasMember

Class(firstYearCourse partial restriction(isTaughtBy allValuesFrom (Professor)))

Class(mathCourse partial restriction(isTaughtBy hasValue (949352)))

Class(academicStaffMember partial restriction (teaches someValuesFrom (undergraduateCourse)))

Class(course partial restriction (isTaughtBy minCardinality (1)))

Class(department partial restriction (hasMember minCardinality(10))

restriction (hasMember maxCardinality(30)))

more examples6
More Examples

Class(course partial complementOf(staffMember))

Class(peopleAtUni complete unionOf(staffMember student))

Class(facultyInCS complete

intersectionOf(faculty

restriction (belongsTo hasValue (CSDepartment))))

Class(adminStaff complete

intersectionOf(staffMember

complementOf(unionOf(faculty techSupportStaff))))

more examples7
More Examples
  • In DL syntax:

course ⊑ ¬staffMember

peopleAtUni ≡ staffMember ⊔ student

facultyInCS ≡ faculty ⊓∃belongsTo.{CSDepartment}

adminStaff ≡ staffMember ⊓

¬(faculty ⊔ techSupportStaff )

Class(course partial complementOf(staffMember))

Class(peopleAtUni complete unionOf(staffMember student))

Class(facultyInCS complete

intersectionOf(faculty

restriction (belongsTo hasValue (CSDepartment))))

Class(adminStaff complete

intersectionOf(staffMember

complementOf(unionOf(faculty techSupportStaff))))

the wine ontology
The Wine Ontology
  • An Ontology describing wine domain
  • One of the most widely used examples for OWL and referenced by W3C.
  • There is also a wine agent associated to this ontology that performs OWL queries using a web-based ontological mark-up language. That is, by combining a logical reasoner with an OWL ontology.
  • The agent's operation can be described in three parts: consulting the ontology, performing queries and outputting results.
  • Available here: http://www.w3.org/TR/owl-guide/
wine ontology schema
Wine Ontology Schema

[http://mysite.verizon.net/jflynn12/VisioOWL/VisioOWL.htm]

wine ontology owl example
Wine Ontology OWL Example

<owl:Class rdf:ID="CheninBlanc">

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#hasColor"/>

<owl:hasValue rdf:resource="#White"/>

</owl:Restriction>

</rdfs:subClassOf>

<rdfs:subClassOf>

<owl:Restriction>

<owl:onProperty rdf:resource="#hasBody"/>

<owl:allValuesFrom>

<owl:Class>

<owl:oneOf rdf:parseType="Collection">

<owl:Thing rdf:about="#Full"/>

<owl:Thing rdf:about="#Medium"/>

</owl:oneOf>

</owl:Class>

</owl:allValuesFrom>

</owl:Restriction>

</rdfs:subClassOf>

<owl:intersectionOf rdf:parseType="Collection">

<owl:Class rdf:about="#Wine"/>

<owl:Restriction>

<owl:onProperty rdf:resource="#madeFromGrape"/>

<owl:hasValue rdf:resource="#CheninBlancGrape"/>

</owl:Restriction>

<owl:Restriction>

<owl:onProperty rdf:resource="#madeFromGrape"/>

<owl:maxCardinality rdf:datatype="http://www.w3.org/2001/XMLSchema#nonNegativeInteger">1</owl:maxCardinality>

</owl:Restriction>

</owl:intersectionOf>

</owl:Class>

<CheninBlanc rdf:ID="VentanaCheninBlanc">

<locatedIn rdf:resource="#CentralCoastRegion"/>

<hasMaker rdf:resource="#Ventana"/>

<hasSugar rdf:resource="#OffDry"/>

<hasFlavor rdf:resource="#Moderate"/>

<hasBody rdf:resource="#Medium"/>

</CheninBlanc>

from description logic to horn logic
From Description Logic to Horn Logic
  • The practical experience in building applications has revealed several shortcomings of OWL, and hence Description Logics for modeling knowledge
  • Feature that ontology engineers are missing:
    • Higher Relational Expressivity
    • Polyadic Predicates
    • Close-World Reasoning
    • Integrity Constraints
    • Modeling Exceptions
  • Proper combination of Description Logic and Horn Logic can define extensions of the language to support such features
    • OWL-Flight
things to keep in mind or summary
Things to keep in mind(or summary)
  • Limitations of RDFS
    • Expressivity limitations
    • Problems with layering
  • Web Ontology Language OWL
    • Design of OWL
    • OWL Layering
    • OWL and Description Logics
    • OWL Syntaxes
further reading
Further Reading
  • Mandatory reading
    • Semantic Web Primer
      • Chapters 4
    • [OWL Guide]
      • http://www.w3.org/TR/owl-guide/
    • Ian Horrocks, Peter F. Patel-Schneider, and Frank van Harmelen. From SHIQ and RDF to OWL: The making of a web ontology language.Journal of Web Semantics, 1(1):7, 2003.
      • http://www.cs.vu.nl/%7Efrankh/abstracts/JWS03.html
  • Further reading
    • Jos de Bruijn: Using Ontologies. Enabling Knowledge Sharing and Reuse on the Semantic Web. DERI Technical Report DERI-2003-10-29, 2003.
      • http://www.deri.org/publications/techpapers/documents/DERI-TR-2003-10-29.pdf
    • [OWL Reference]
      • http://www.w3.org/TR/owl-ref/
    • [OWL Abstract syntax and Semantics]
      • http://www.w3.org/TR/owl-semantics
    • J. de Bruijn, A. Polleres, R. Lara, and D. Fensel: OWL DL vs. OWL Flight: Conceptual modeling and reasoning on the semantic web. In Proceedings of the 14th International World Wide Web Conference (WWW2005), Chiba, Japan, 2005. ACM.