Ontologies in RDF-S/OWL

Emanuele Della Valle
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http://emanueledellavalle.org
Ontologies in RDF-S/OWL

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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="Rodin">
<sculpts resource="TheKiss"/>
</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) ]

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)]

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

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Ontologies in RDF-S/OWL

by Emanuele Della Valle on Jul 04, 2010

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Ontologies in RDF-S/OWL — Presentation Transcript