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Ontologies in RDF-S/OWL
 

Ontologies in RDF-S/OWL

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  • 07/04/10 © 2005 - Della Valle - CEFRIEL
  • 07/04/10 © 2005 - Della Valle - CEFRIEL
  • 07/04/10 © 2005 - Della Valle - CEFRIEL
  • 07/04/10 © 2005 - Della Valle - CEFRIEL
  • @prefix rdfs: . @prefix ex: . @prefix owl: . ex:Artist a owl:Class . ex:Piece a owl:Class . ex:Sculptor a owl:Class . ex:Sculptor rdfs:subClassOf ex:Artist . ex:creates a owl:ObjectProperty . ex:creates rdfs:domain ex:Artist . ex:Rodin a ex:Sculptor . ex:TheKiss a ex:Piece . ex:Rodin ex:creates ex:TheKiss .
  • RDF/Description[@about='Rodin']/sculpts/@resource RDF/Description[sculpts/@resource='TheKiss']/@about

Ontologies in RDF-S/OWL Ontologies in RDF-S/OWL Presentation Transcript

    • Emanuele Della Valle
    • [email_address]
    • http://emanueledellavalle.org
    Ontologies in RDF-S/OWL
  • Share, Remix, Reuse — Legally
    • This work is licensed under the Creative Commons Attribution 3.0 Unported License.
    • Your are free:
      • to Share — to copy, distribute and transmit the work
      • to Remix — to adapt the work
    • Under the following conditions
      • Attribution — You must attribute the work by inserting
        • “ © applied-semantic-web.org” at the end of each reused slide
        • a credits slide stating: these slides are partially based on “Ontologies in RDF-S/OWL” by Emanuele Della Valle http://applied-semantic-web.org/2010/03/03_RDFS-OWL.ppt
    • To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/
  • Ontology: RDF-S and OWL
  • RDF-S/OWL in a nutshell Ontology definition
    • Philosophy (400BC):
      • Systematic explanation of Existence
    • Neches (91):
      • Ontology defines basic terms and relations comprising the vocabulary of a topic area as well as the rules for combining terms and relations to define extensions to the vocabulary
    • Gruber (93):
      • Explicit specification of a conceptualization
    • Borst (97):
      • Formal specification of a shared conceptualization
    • Studer(98)
      • Formal, explicit specification of a shared conceptualization
  • RDF-S/OWL in a nutshell What does it mean? Formal, explicit specification of a shared conceptualization Machine readable Several people agrees that such conceptual model is adequate to describe such aspects of the reality A conceptual model of some aspects of the reality It makes domain assumption explicit
  • RDF-S/OWL in a nutshell Questa è un’ontologia?
    • NO, perchè
      • È una concettualizzazione
      • È condivisa dalla comunità che l’ha sviluppata
    • … ma non è
      • esplicita (la dimensione dei rami molto probabilmente non indica la numerosità delle speci)
      • formale (nessuna macchina può usarla)
  • RDF-S/OWL in a nutshell Esempio di ontologia
    • Concetti e relazioni primitivi
      • essere umano
      • maschio
      • femmina
      • ha figlio
    • Concetti e relazioni derivate
      • un uomo è un essere umano ed è un maschio
      • una donna è un essere umano ed è una femmina
      • una madre è una donna che ha almeno un figlio
      • una padre è un uomo che ha almeno un figlio
      • un genitore è o un padre o una madre
      • un nonno è un uomo che ha almeno un figlio che è un genitore
      • “ essere figlio di ” è la relazione inversa a “avere un figlio”
    • Fatti asseriti
      • Antonio , Lorenzo e Carlo sono uomini
      • Rosanna è una donna
      • Antonio ha figlio Lorenzo
      • Rosanna ha figlio Carlo
      • Carlo è figlio di Lorenzo
      • Una macchina in grado di “capire” un linguaggio ontologico “sa inferire”
      • Concetti: un nonno è un genitore
      • Fatti: Antonio è un nonno, Lorenzo è un padre, Rosanna è una madre
  • RDF-S/OWL in a nutshell Linguaggio Ontologico
    • Concetti e relazioni primitivi
      • essere umano
      • maschio
      • femmina
      • ha figlio
    • Concetti e relazioni derivate
      • un uomo è un essere umano ed è un maschio
      • una donna è un essere umano ed è una femmina
      • una madre è una donna che ha almeno un figlio
      • una padre è un uomo che ha almeno un figlio
      • un genitore è o un padre o una madre
      • un nonno è un uomo che ha almeno un figlio che è un genitore
      • “ essere figlio di” è la relazione inversa a “avere un figlio”
    • Fatti asseriti
      • Antonio , Lorenzo e Carlo sono uomini
      • Rosanna è una donna
      • Antonio ha figlio Lorenzo
      • Rosanna ha figlio Carlo
      • Carlo è figlio di Lorenzo
      • Una macchina in grado di “capire” un linguaggio ontologico “sa inferire”
      • Concetti: un nonno è un genitore
      • Fatti: Antonio è un nonno, Lorenzo è un padre, Rosanna è una madre
  • RDF-S/OWL in a nutshell Le parti di un linguaggio ontologico
    • concetti
      • astrazioni del dominio applicativo tipicamente visti come insiemi
    • relazioni
      • esprimono l’esistenza di relazioni tra i concetti del dominio tipicamente viste come relazioni binarie tra gli individui
    • assiomi
      • formalizzano quali combinazioni di concetti e relazioni sono ammissibili
    • individui
      • elementi degli insiemi definiti dai concetti
    • asserzioni
      • dichiarano l’appartenenza di un individuo ad un insieme
    • fatti
      • legano due individui tramite una relazione
  • RDF-S/OWL in a nutshell Strong vs. Weak Semantics? “ A little semantics , goes a long way” [James Hendler, 2001] “ A Little Semantic Web Goes a Long Way in Biology” [ Wolstencroft et al., 2005]
  • RDF-S/OWL in a nutshell A simple ontology Artist Piece Painter Paint paints Sculptor Sculpt sculpts creates
  • RDF-S/OWL in a nutshell Specifying classes, sub-classes and instances
    • Creating a class
      • RDFS: Artist rdf:type owl:Class .
      • FOL:  x Artist(x)
    • Creating a subclass
      • RDFS: Painter rdfs:subClassOf Artist .
      • RDFS: Sculptor rdfs:subClassOf Artist .
      • FOL:  x [Painter(x)  Sculptor(x)  Artist(x)]
    • Creating an instance
      • RDFS: Rodin rdf:type Sculptor .
      • FOL: Sculptor(Rodin)
    Artist Painter Sculptor Rodin
    • Creating a property
      • RDFS: creates rdf:type owl:ObjectProperty .
      • FOL:  x  y Creates(x,y)
    • Using a property
      • RDFS: Rodin creates TheKiss .
      • FOL: Creates(Rodin, TheKiss)
    • Creating subproperties
      • RDFS: paints rdfs:subPropertyOf creates .
      • FOL:  x  y [Paints(x,y)  Creates(x,y)]
      • RDFS: sculpts rdfs:subPropertyOf creates .
      • FOL:  x  y [Sculpts(x,y)  Creates(x,y)]
    RDF-S/OWL in a nutshell Specifying properties and sub-properties - - creates paints
    • È abbastanza importante parlare di OWL import e la parte di metadati di un’ontologia altrimenti non si possono validare le ontologie con http://owl.cs.manchester.ac.uk/validator/
  • RDF-S/OWL in a nutshell Specifying domain/range constrains
    • Checking which classes and properties can be use together
    • RDFS:
      • creates rdfs:domain Artist .
      • creates rdfs:range Piece .
      • paints rdfs:domain Painter .
      • paints rdfs:range Paint .
      • sculpts rdfs:domain Sculptor .
      • sculpts rdfs:range Sculpt .
    • FOL:
      •  x  y [Creates(x,y)  Artist(x)  Piece(y)]
      •  x  y [Paints(x,y)  Painter(x)  Paint(y)]
      •  x  y [Sculpts(x,y)  Sculptor(x)  Sculpt(y)]
  • RDF-S/OWL in a nutshell The ontology we specified Artist Piece Painter Paint paints Sculptor Sculpt sculpts creates
  • RDF-S/OWL in a nutshell RDF-S semantics (a part of it)
    • if then
      • x rdfs:subClassOf y . a rdf:type y . a rdf:type x .
      • x rdfs:subClassOf y . x rdfs:subClassOf z . y rdfs:subClassOf z .
      • x a y . x b y . a rdfs:subPropertyOf b .
      • a rdfs:subPropertyOf b . a rdfs:subPropertyOf c . b rdfs:subPropertyOf c .
      • x a y . x rdf:type z . a rdfs:domain z .
      • x a u . u rdf:type z . a rdfs:range z .
      • Read out more in RDF Semantics http://www.w3.org/TR/rdf-mt/
  • RDF-S/OWL in a nutshell RDF-S semantics at work
    • Shared the ontology ...
      • @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
      • @prefix ex: <http://www.ex.org/schema#> .
      • ex:Sculptor rdfs:subClassOf ex:Artist .
      • ex:Painter rdfs:subClassOf ex:Artist .
      • ex:Sculpt rdfs:subClassOf ex:Piece.
      • ex:Painting rdfs:subClassOf ex:Piece .
      • ex:creates rdfs:domain ex:Artist .
      • ex:creates rdfs:range ex:Piece.
      • ex:sculpts rdfs:subPropertyOf ex:creates .
      • ex:sculpts rdfs:domain ex:Sculptor .
      • ex:sculpts rdfs:range ex:Sculpt .
    • ... when transmitting the following triple …
      • ex:Rodin ex:sculpts ex:TheKiss .
  • RDF-S/OWL in a nutshell Without Inference
    • A recipient, that only understands XML syntax,
    • receiving
        • <RDF>
        • <Description about=&quot;Rodin&quot;>
        • <sculpts resource=&quot;TheKiss&quot;/>
        • </Description>
        • </RDF>
    • can answer the following queries
      • What does Rodin sculpt?
        • RDF/Description[@about='Rodin']/sculpts/@resource
      • Who does sculpt TheKiss?
        • RDF/Description[sculpts/@resource='TheKiss']/@about
      • Try out your self at http://www.mizar.dk/XPath/
    • but it cannot answer
      • Who is Rodin?
      • What is TheKiss?
      • Is there any Sculptor/Scupts?
      • Is there any Artist/Piece?
  • RDF-S/OWL in a nutshell Knowing the ontology and RDF-S semantics …
    • A recipient, that knows the ontology and “understands” RDF semantics ,
      • Receiving Rodin sculpts TheKiss .
    Rodin TheKiss Artist Piece Painter Paint paints Sculptor Sculpt sculpts creates
  • RDF-S/OWL in a nutshell … a reasoner can answer
    • the previous queries
      • What does Rodin sculpt?
        • ex:TheKiss
      • Who does sculpt TheKiss?
        • ex:Rodin
    • it can also answer
      • Who is Rodin?
        • ex:Artist, ex:Sculptor, rdfs: Resource
      • What is TheKiss?
        • ex:Sclupt, ex:Piece, rdfs: Resource
      • Is there any Sculptor?
        • ex:Rodin
      • Is the any Artist?
        • ex:Rodin
      • Is there any Sculpt?
        • ex:TheKiss
      • Is there any Piece?
        • ex:TheKiss
      • Is there any Paint?
        • 0 results
      • Is there any Painter?
        • 0 results
  • RDF-S/OWL in a nutshell More expressive power 1/3
    • RDFS is a light ontological language that allows for defining simple vocabularies.
    • One may want also express
      • Cardinality constrains (max, min, exactly) for properties usage
        • Es. a Polygon has 3 or more edges
        •  x [Polygon(x)  ≥3y Edge(y)  Forms(y,x) ]
      • Property types
        • transitive
          • e.g. hasAncestor is a transitive property: if A hasAncestor B and B hasAncestor C , then A hasAncestor C .
          •  x  y  z [HasAncestor(x,y)  HasAncestor(y,z)  HasAncestor(x,z) ]
        • inverse
          • e.g. sclupts has isSculptedBy as inverse property: if A sclupts B then B isSculptedBy A
          •  x  y [Sculpts(x,y)  IsSculptedBy(y,x) ]
  • RDF-S/OWL in a nutshell More expressive power 2/3
        • simmetric
          • e.g. isCloseTo is a simmetric property: if A isCloseTo B then B isCloseTo A
          •  x  y [IsCloseTo(x,y)  IsCloseTo(y,x) ]
      • Restrictions of usage for a specific property
        • All values of property must be of a certain kind
          • e.g. a D.O.C. Wine can be only produced by a Certified Wienery
          •  x  y [DOCWine(x)  Produces(x,y)  CertifiedWienery(y)]
        • Some values of property must be of a certain kind
          • e.g. a Famous Painter must have painted some Famous Painting
          •  x [FamousPainter(x)   y FamousPaint(y)  IsPaintedBy(y,x)]
      • A class is defined combining other classes (union, intersection, negation, ...)
        • A white wine is a Wine and its color is “white”
        •  x [Wine(x)  White(x)]
  • RDF-S/OWL in a nutshell More expressive power 3/3
      • Two instances refers to the same real object
        • “ The Boss” and “Bruce Springsteen” are two names for the same person
        • TheBoss = BruceSpringsteen
      • Two classes refers to the same set
        • “ Painters” in english and “Pittori” in italian
        •  x [Painter(x)  Pittore(x)]
      • Two properties refers to the same binary relationship
        • “ Paints” in english and “Dipinge” in italian
        •  x  y [Paints(x,y)  Dipinge(x,y)]
  • RDF-S/OWL in a nutshell Expressivity vs. Tractability
    • The more an ontological language is expressive the less is tractable
    • the Web Ontology Language (OWL) comes with several profiles that offers different trade-offs between expressivity and tractability.
  • RDF-S/OWL in a nutshell OWL 2 profiles
    • OWL 1 defines only one fragment (OWL Lite)
      • And it isn’t very tractable!
    • OWL 2 defines several different fragments with
      • Useful computational properties
        • E.g., reasoning complexity in range LOGSPACE to PTIME
      • Useful implementation possibilities
        • E.g., Smaller fragments implementable using RDBs
    • OWL 2 profiles
      • OWL 2 EL, OWL 2 QL, OWL 2 RL
  • RDF-S/OWL in a nutshell OWL 2 EL
    • Useful for applications employing ontologies that contain very
    • large number of properties and/or classes
      • Captures expressive power used by many large-scaleontologies E.g.; SNOMED CT, NCI thesaurus
    • Features
      • Included: existential restrictions, intersection, subClass,equivalentClass, disjointness, range and domain, object property inclusion possibly involving property chains, and data property inclusion, transitive properties, keys …
      • Missing: include value restrictions, Cardinality restrictions (min, max and exact), disjunction and negation
    • Maximal language for which reasoning (including query answering) known to be worst-case polynomial
  • RDF-S/OWL in a nutshell OWL 2 QL
    • Useful for applications that use very large volumes of data, and where query answering is the most important task
    • Captures expressive power of simple ontologies like thesauri, classifications, and (most of) expressive power of ER/UML schemas
    • E.g., CIM10, Thesaurus of Nephrology, ...
    • Features
      • Included: limited form of existential restrictions, subClass, equivalentClass, disjointness, range & domain, symmetric properties, …
      • Missing: existential quantification to a class, self restriction, nominals, universal quantification to a class, disjunction etc.
    • Can be implemented on top of standard relational DBMS
    • Maximal language for which reasoning (including query answering) is known to be worst case logspace (same as DB)
  • RDF-S/OWL in a nutshell OWL 2 RL
    • Useful for applications that require scalable reasoning without sacrifying too much expressive power, and where query answering is the most important task
    • Support most OWL features but
      • with restrictions placed on the syntax of OWL 2
      • standard semantics only apply when they are used in a restricted way
    • Can be implemented on top of rule extended DBMS
      • E.g., Oracle’s OWL Prime implemented using forward chaining rules in Oracle 11g
      • Related to DLP and pD*
    • Allows for scalable ( polynomial) reasoning using rule-based technologies
  • RDF-S/OWL in a nutshell RDF -S/OWL Resources
    • OWL Frequently Asked Questions
      • http://www.w3.org/2003/08/owlfaq.html
    • RDF-S/OWL implementations - community maintained list of open-source and commercial SPARQL engines
      • http://esw.w3.org/topic/SemanticWebTools#head-d07454b4f0d51f5e9d878822d911d0bfea9dcdfd
    • RDF-S Specification
      • http://www.w3.org/TR/rdf-schema/
    • OWL Working Group Wiki
      • http://www.w3.org/2007/OWL/wiki