Modulo3 Modulo3 Linguaggi: OWLLinguaggi: OWL

UNIVERSITA’ DI CAMERINOCorso di laurea in Informatica (classe 23/S)

Barbara Rebarbara.re@unicam.it

Anno Accademico 2007-08

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Agenda

Introduzione a OWL

Classi OWL

Proprietà OWL

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Linguaggi

I linguaggi forniscono meccanismi base che possono essere usati per rappresentare la semantica delle informazioni necessarie per il Semantic Web

XML RDF RDF(S)

OWLOWL OWL 1.1OWL 1.1

XML

RDF

RDF(S)

OWL AN

NO

TA

ZIO

NE

INTEG

RA

ZIO

NE

INFE

REN

ZA

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Origini di OWL

DAML

DAML+OIL

DAML = DARPA Agent Markup LanguageOIL = Ontology Inference Layer

OIL

OWL

RDF

Tutti influenzati da RDF

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OWL – principi fondamentali

OWL aggiunge ulteriori vocaboli per descrivere proprietà e classi

Relazioni tra classi (es. disjointness)Cardinalità (es. "exactly one")UguaglianzaTipi di proprietà più ricchiCaratteristiche delle proprietà (es. symmetry)Elencazione delle classi

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Non tutti hanno bisogno di tutta l’espressività di OWL

OWL Full

OWL DL

OWL Lite

Le tre facce di OWL

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OWL Sottolinguaggi

OWL Little supporta gli utenti per necessità di classificazione e gerarchia attraverso vincoli semplici

Attraverso semplici PATH è possibile migrare da thesauri e tassonomie a OWL LittleE’ possibile esprimere 0 e 1 come valori di cardinalità

OWL DL supporta gli utente che vogliono massima espressività mentre conservano completezza (tutte le conclusioni sono garantite essere computabili) e decidibilità (tutte le computazioni finiscono in un tempo finito) computazionale

Sono definite corrispondenze specifiche con la description logics – campo di ricerca che ha studiato la formulazione formale di OWL

OWL Full è inteso per gli utenti che vogliono massima espressività e al tempo stesso la libertà sintattica di RDF senza garanzie computazionali

Non tutti i reasoning sono in grado di processare l’espressività di OWL Full

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Relazioni tra l’espressività

Un’ontologia valida in OWL Lite è un’ontologia legale in OWL DL

Un’ontologia valida in OWL DL è un’ontologia legale in OWL Full

Ogni conclusione valida in OWL Lite è una conclusione valida anche in OWL DL

Ogni conclusione valida in OWL DL è una conclusione valida anche in OWL Full

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OWL namespace

The built-in vocabulary for OWL all comes from the OWL namespace

http://www.w3.org/2002/07/owl#

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OWL Classes

Le classi forniscono un meccanismo astratto per raggruppare risorse con simili caratteristiche

Ogni classe è implicitamente sottoclassse di owl:Think

Class descriptionSemplici riferimenti alle classi

Class axiomsIntroduce ulteriori componenti che sono necessari o sufficienti per caratterizzare la classe

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Tipi di class description

OWL distinguishes six types of class descriptions: a class identifier (a URI reference)

Descrive la classe introducendo un nome

an exhaustive enumeration of individuals that together form the instances of a class a property restriction the intersection of two or more class descriptions the union of two or more class descriptions the complement of a class description

Descrivono la classe introducendo vincoli sulla sua estenzione

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Class identifier

<owl:Class rdf:ID="Human"/>

owl:Class è una sottoclasse di rdfs:Class

"ex:Human rdf:type owl:Class ." è la tripla che esprime

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Class enumerate

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

<owl:Thing rdf:about="#Eurasia"/> <owl:Thing rdf:about="#Africa"/> <owl:Thing rdf:about="#NorthAmerica"/> <owl:Thing rdf:about="#SouthAmerica"/> <owl:Thing rdf:about="#Australia"/> <owl:Thing rdf:about="#Antarctica"/>

</owl:oneOf></owl:Class>

Fa riferimento ad una classe che contiene esattamente gli individui elencati

La classe "enumeration" è definita utilizzando la proprietà owl:oneOf.

I valori associati alla classe deve essere una lista di individui che sono istanze della classe

Questo permette alla classe di descrivere attraverso una enumerazione esaustiva le sue istanze.

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Property restriction

Classe di individui che soddisfano una particolare restrizione sulla proprietà Una restrizione di proprietà è un tipo speciale di descrittore di classe, una classe

anonima di tutti gli individui che soddisfano la restrizione

<owl:Restriction> <owl:onProperty rdf:resource="(some property)" /> (precisely one value or cardinality constraint, see below)</owl:Restriction>

OWL distingue due tipi di restrizioniVincoli sul valore che introduce vincoli sulle proprietà quando vengono applicate a particolari descrittori di classe

Si può far riferimento a quei individui il cui valore della proprietà adjacentTo dovrebbero essere alcune Regioni, ed usare questa come una classe assioma per la regione stessaATT: è differente da rdfs:range che deve esse applicata a tutte le situazioni in cui la proprietà è usata

Un vincolo di cardinalità introduce vincoli sul numero di valori che la proprietà può assumere nel contesto di una particolare descrizione di una classe

Si può introdurre una relazione hasPlayer per una squadra di calcio ed una squadra di baseball

Intersection, union and complement

Può essere riferito sia a datatype property che a object property

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Value Constraints

owl:allValuesFrom <owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /><owl:allValuesFrom rdf:resource="#Human" /></owl:Restriction>

Owl:someValuesFrom<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /><owl:someValuesFrom rdf:resource="#Physician" /></owl:Restriction>

Owl:hasValue<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /> <owl:hasValue rdf:resource="#Clinton" /></owl:Restriction>

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Wine and Winery

<owl:Class rdf:ID="Wine"> <rdfs:subClassOf

rdf:resource="&food;PotableLiquid" /> ...

<rdfs:subClassOf>

<owl:Restriction> <owl:onProperty

rdf:resource="#hasMaker" /> <owl:allValuesFrom

rdf:resource="#Winery" />

</owl:Restriction> </rdfs:subClassOf> ...</owl:Class>

<owl:Class rdf:ID="Wine"><rdfs:subClassOf

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

<owl:Restriction> <owl:onProperty rdf:resource="#hasMaker" /> <owl:someValuesFrom

rdf:resource="#Winery" />

</owl:Restriction>

</rdfs:subClassOf> ... </owl:Class>  

Relation Implications

allValuesFromFor all wines, if they have makers, all the makers are

wineries.

someValuesFrom  

For all wines, they have at least one maker that is a winery.

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Cardinality constraints

owl:maxCardinality

<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /> <owl:maxCardinality rdf:datatype="&xsd;nonNegativeInteger">2</owl:maxCardinality></owl:Restriction>

owl:minCardinality

<owl:Restriction> <owl:onProperty rdf:resource="#hasParent" /><owl:minCardinality

rdf:datatype="&xsd;nonNegativeInteger">2</owl:minCardinality></owl:Restriction>

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Intersection

Descrive la classe la cui estensione vincola precisamente gli individui che sono membri dell’estensione di tutte le classi introdotte nella lista

<owl:Class rdf:ID="WhiteWine"> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Wine" /> <owl:Restriction> <owl:onProperty rdf:resource="#hasColor" /> <owl:hasValue rdf:resource="#White" /> </owl:Restriction> </owl:intersectionOf></owl:Class>

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union

Descrive la classe la cui estensione vincola precisamente gli individui che sono membri dell’estensione di almeno una delle classi introdotte nella lista

<owl:Class rdf:ID="Fruit"> <owl:unionOf rdf:parseType="Collection"> <owl:Class rdf:about="#SweetFruit" /> <owl:Class rdf:about="#NonSweetFruit" /> </owl:unionOf></owl:Class>

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Complement

Descrive la classe la cui estensione vincola precisamente gli individui che non sono membri delle classi introdotte nella lista

The expression "not meat" could be written as

<owl:Class> <owl:complementOf>

<owl:Class rdf:about="#Meat"/> </owl:complementOf>

</owl:Class>

<owl:Class rdf:ID="ConsumableThing" />

<owl:Class rdf:ID="NonConsumableThing"> <owl:complementOf rdf:resource="#ConsumableThing" /> </owl:Class>

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Class axioms

OWL contiene tre costrutti del linguaggio per combinare la class descriptions in class axioms

Fa riferimento ad elementi addizionali che sono necessari e/o sufficienti per descrivere la classe

rdfs:subClassOf allows one to say that the class extension of a class description is a subset of the class extension of another class description

<owl:Class rdf:ID="Opera"> <rdfs:subClassOf rdf:resource="#MusicalWork" /></owl:Class>

owl:equivalentClass allows one to say that a class description has exactly the same class extension as another class description.

<owl:Class rdf:about="#US_President"> <owl:equivalentClass rdf:resource="#PrincipalResidentOfWhiteHouse"/></owl:Class>

owl:disjointWith allows one to say that the class extension of a class description has no members in common with the class extension of another class description

<owl:Class rdf:about="#Man"> <owl:disjointWith rdf:resource="#Woman"/></owl:Class>

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Properties

OWL distinguishes between two main categories of properties that an ontology builder may want to define

Object properties link individuals to individualsDatatype properties link individuals to data values

<owl:ObjectProperty rdf:ID="hasParent"/>

Property axioms define additional characteristics of properties OWL supports the following constructs for property axioms

RDF Schema constructs: rdfs:subPropertyOf, rdfs:domain and rdfs:range relations to other properties: owl:equivalentProperty and owl:inverseOf global cardinality constraints: owl:FunctionalProperty and owl:InverseFunctionalProperty logical property characteristics: owl:SymmetricProperty and owl:TransitiveProperty

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RDF Schema constructs

rdfs:subPropertyOf axiom defines that the property is a subproperty of some other property

Formally this means that if P1 is a subproperty of P2, then the property extension of P1 (a set of pairs) should be a subset of the property extension of P2 (also a set of pairs)

rdfs:domain is a built-in property that links a property (some instance of the class rdf:Property) to a class description

An rdfs:domain axiom asserts that the subjects of such property statements must belong to the class extension of the indicated class description

rdfs:range is a built-in property that links a property (some instance of the class rdf:Property) to to either a class description or a data range

An rdfs:range axiom asserts that the values of this property must belong to the class extension of the class description or to data values in the specified data range.

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subPropertyOf - esempio

<owl:ObjectProperty rdf:ID="hasMother"> <rdfs:subPropertyOf rdf:resource="#hasParent"/></owl:ObjectProperty>

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rdfs:domain - esempio

<owl:ObjectProperty rdf:ID="hasBankAccount"> <rdfs:domain>

<owl:Class> <owl:unionOf rdf:parseType="Collection">

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

rdf:about="#Corporation"/> </owl:unionOf> </owl:Class>

</rdfs:domain></owl:ObjectProperty>

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Relations to other properties

owl:equivalentProperty construct can be used to state that two properties have the same property extension

owl:inverseOf construct can be used to define such an inverse relation between properties

<owl:ObjectProperty rdf:ID="hasChild"> <owl:inverseOf rdf:resource="#hasParent"/></owl:ObjectProperty>

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Global cardinality constraints

A functional property is a property that can have only one (unique) value y for each instance x

There cannot be two distinct values y1 and y2 such that the pairs (x,y1) and (x,y2) are both instances of this property

<owl:ObjectProperty rdf:ID="husband"> <rdf:type rdf:resource="&owl;FunctionalProperty" /><rdfs:domain rdf:resource="#Woman" /><rdfs:range rdf:resource="#Man" /></owl:ObjectProperty>

If a property is declared to be inverse-functional, then the object of a property statement uniquely determines the subject (some individual)

If we state that P is an owl:InverseFunctionalProperty, then this asserts that a value y can only be the value of P for a single instance x

There cannot be two distinct instances x1 and x2 such that both pairs (x1,y) and (x2,y) are instances of P.

<owl:InverseFunctionalProperty rdf:ID="biologicalMotherOf"> <rdfs:domain rdf:resource="#Woman"/> <rdfs:range rdf:resource="#Human"/></owl:InverseFunctionalProperty>

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Logical property characteristics

owl:TransitiveProperty When one defines a property P to be a transitive property, this means that if

a pair (x,y) is an instance of P, and the pair (y,z) is also instance of P, then we can infer the the pair (x,z) is also an instance of P

<owl:ObjectProperty rdf:ID="subRegionOf"> <rdf:type rdf:resource="&owl;TransitiveProperty"/> <rdfs:domain rdf:resource="#Region"/> <rdfs:range rdf:resource="#Region"/></owl:ObjectProperty>

owl:symmentricalProperty A symmetric property is a property for which holds that if the pair (x,y) is an

instance of P, then the pair (y,x) is also an instance of P

<owl:SymmetricProperty rdf:ID="friendOf"> <rdfs:domain rdf:resource="#Human"/> <rdfs:range rdf:resource="#Human"/></owl:SymmetricProperty>

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Individual

Individuals are defined with individual axioms (also called "facts")

We discuss two types of factsFacts about class membership and property values of individuals Facts about individual identity

OWL provides three constructs for stating facts about the identity of individuals

owl:sameAs is used to state that two URI references refer to the same individualowl:differentFrom is used to state that two URI references refer to different individuals owl:AllDifferent provides an idiom for stating that a list of individuals are all different

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Individual istanziazione

Facts about class membership and property values of individuals

<Opera rdf:ID="Tosca"> <hasComposer rdf:resource="#Giacomo_Puccini"/> <hasLibrettist rdf:resource="#Victorien_Sardou"/> <hasLibrettist rdf:resource="#Giuseppe_Giacosa"/> <hasLibrettist rdf:resource="#Luigi_Illica"/> <premiereDate rdf:datatype="&xsd;date">1900-01-14</premiereDate> <premierePlace rdf:resource="#Roma"/> <numberOfActs rdf:datatype="&xsd;positiveInteger">3</numberOfActs>

</Opera>

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Owl:sameAs - esempio

<rdf:Description rdf:about="#William_Jefferson_Clinton"> <owl:sameAs rdf:resource="#BillClinton"/></rdf:Description>

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owl:AllDifferent - esempio

<owl:AllDifferent> <owl:distinctMembers rdf:parseType="Collection"> <Opera rdf:about="#Don_Giovanni"/> <Opera rdf:about="#Nozze_di_Figaro"/> <Opera rdf:about="#Cosi_fan_tutte"/> <Opera rdf:about="#Tosca"/> <Opera rdf:about="#Turandot"/> <Opera rdf:about="#Salome"/> </owl:distinctMembers></owl:AllDifferent>

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owl:differentFrom - esempio

<Opera rdf:ID="Don_Giovanni"/>

<Opera rdf:ID="Nozze_di_Figaro"> <owl:differentFrom rdf:resource="#Don_Giovanni"/></Opera>

<Opera rdf:ID="Cosi_fan_tutte"> <owl:differentFrom rdf:resource="#Don_Giovanni"/> <owl:differentFrom rdf:resource="#Nozze_di_Figaro"/></Opera>

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Datatype

Focusing on the notion of a data range for specifying a range of data values

OWL allows three types of data range specificationsA RDF datatype specificationThe RDFS class rdfs:LiteralAn enumerated datatype, using the owl:oneOf construct (permette di mettere in alternativa i datatype RDF)

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Per approfondimenti

OWL Web Ontology Language Reference

W3C Recommendation 10 February 2004

http://www.w3.org/TR/2004/REC-owl-ref-20040210/

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OWL 1.1

OWL 1.1 extends the W3C OWL Web Ontology Language with a small but useful set of features that have been requested by users, for which effective reasoning algorithms are now available, and that OWL tool developers are willing to support

The new features include extra syntactic sugaradditional property and qualified cardinality constructorsextended datatype supportsimple metamodellingextended annotations

OWL 1.1 Web Ontology LanguageStructural Specification and Functional-Style Syntax

Editor's Draft of 23 May 2007This version: http://www.webont.com/owl/1.1/owl_specification.html

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