ontology languages - pierre senellart · 2012. 9. 7. · 3 / 43 télécom paristech pierre...

7 September 2012, Télécom ParisTech

Ontology Languages

Pierre Senellart

2 / 43 Télécom ParisTech Pierre Senellart

Outline

IntroductionThe Semantic WebOntologies and ReasoningComponents of an Ontology

3 Ontology Languages for the WebRDFRDFSOWL

Querying Data through Ontologies

Reference Material


Outline


3 Ontology Languages for the Web


Reference Material


Outline




Reference Material


The Semantic Web

A Web in which the resources are semantically describedannotations give information about a page, explain an expression ina page, etc.

More precisely, a resource is anything that can be referred to by aURI

a web page, identified by a URLa fragment of an XML document, identified by an element node ofthe document,a web service,a thing, an object, a concept, a property, etc.

Semantic annotations: logical assertions that relate resources tosome terms in associated ontologies


Outline




Reference Material


Ontologies

Formal descriptions providing human users a sharedunderstanding of a given domain

A controlled vocabulary

Formally defined so that it can also be processed by machines

Logical semantics that enables reasoning

Reasoning is the key for different important tasks of Web datamanagement, in particular:

to answer queries (over possibly distributed data)to relate objects in different data sources enabling their integrationto detect inconsistencies or redundanciesto refine queries with too many answers, or to relax queries with noanswer


Where Do Ontologies Come From?

Manually crafted to represent the knowledge of a specific domain(e.g., life sciences)

Exported from classical Web databases

Through information extraction from the Web, Wikipedia, etc.(e.g., DBpedia, YAGO)

Private to a company or public

Some ontologies focus on instances, others on a schema (seefurther)

Value of the Semantic Web: bits of ontologies can be re-used inanother, and ontologies can be mapped through an owl:sameAslink

As of September 2011

MusicBrainz

(zitgist)

P20

Turismo de

Zaragoza

yovisto

Yahoo! Geo

Planet

YAGO

World Fact-book

El ViajeroTourism

WordNet (W3C)

WordNet (VUA)

VIVO UF

VIVO Indiana

VIVO Cornell

VIAF

URIBurner

Sussex Reading

Lists

Plymouth Reading

Lists

UniRef

UniProt

UMBEL

UK Post-codes

legislationdata.gov.uk

Uberblic

UB Mann-heim

TWC LOGD

Twarql

transportdata.gov.

uk

Traffic Scotland

theses.fr

Thesau-rus W

totl.net

Tele-graphis

TCMGeneDIT

TaxonConcept

Open Library (Talis)

tags2con delicious

t4gminfo

Swedish Open

Cultural Heritage

Surge Radio

Sudoc

STW

RAMEAU SH

statisticsdata.gov.

uk

St. Andrews Resource

Lists

ECS South-ampton EPrints

SSW Thesaur

us

SmartLink

Slideshare2RDF

semanticweb.org

SemanticTweet

Semantic XBRL

SWDog Food

Source Code Ecosystem Linked Data

US SEC (rdfabout)

Sears

Scotland Geo-

graphy

ScotlandPupils &Exams

Scholaro-meter

WordNet (RKB

Explorer)

Wiki

UN/LOCODE

Ulm

ECS (RKB

Explorer)

Roma

RISKS

RESEX

RAE2001

Pisa

OS

OAI

NSF

New-castle

LAASKISTI

JISC

IRIT

IEEE

IBM

Eurécom

ERA

ePrints dotAC

DEPLOY

DBLP (RKB

Explorer)

Crime Reports

UK

Course-ware

CORDIS (RKB

Explorer)CiteSeer

Budapest

ACM

riese

Revyu

researchdata.gov.

ukRen. Energy Genera-

tors

referencedata.gov.

uk

Recht-spraak.

nl

RDFohloh

Last.FM (rdfize)

RDF Book

Mashup

Rådata nå!

PSH

Product Types

Ontology

ProductDB

PBAC

Poké-pédia

patentsdata.go

v.uk

OxPoints

Ord-nance Survey

Openly Local

Open Library

OpenCyc

Open Corpo-rates

OpenCalais

OpenEI

Open Election

Data Project

OpenData

Thesau-rus

Ontos News Portal

OGOLOD

JanusAMP

Ocean Drilling Codices

New York

Times

NVD

ntnusc

NTU Resource

Lists

Norwe-gian

MeSH

NDL subjects

ndlna

myExperi-ment

Italian Museums

medu-cator

MARC Codes List

Man-chester Reading

Lists

Lotico

Weather Stations

London Gazette

LOIUS

Linked Open Colors

lobidResources

lobidOrgani-sations

LEM

LinkedMDB

LinkedLCCN

LinkedGeoData

LinkedCT

LinkedUser

FeedbackLOV

Linked Open

Numbers

LODE

Eurostat (OntologyCentral)

Linked EDGAR

(OntologyCentral)

Linked Crunch-

base

lingvoj

Lichfield Spen-ding

LIBRIS

Lexvo

LCSH

DBLP (L3S)

Linked Sensor Data (Kno.e.sis)

Klapp-stuhl-club

Good-win

Family

National Radio-activity

JP

Jamendo (DBtune)

Italian public

schools

ISTAT Immi-gration

iServe

IdRef Sudoc

NSZL Catalog

Hellenic PD

Hellenic FBD

PiedmontAccomo-dations

GovTrack

GovWILD

GoogleArt

wrapper

gnoss

GESIS

GeoWordNet

GeoSpecies

GeoNames

GeoLinkedData

GEMET

GTAA

STITCH

SIDER

Project Guten-berg

MediCare

Euro-stat

(FUB)

EURES

DrugBank

Disea-some

DBLP (FU

Berlin)

DailyMed

CORDIS(FUB)

Freebase

flickr wrappr

Fishes of Texas

Finnish Munici-palities

ChEMBL

FanHubz

EventMedia

EUTC Produc-

tions

Eurostat

Europeana

EUNIS

EU Insti-

tutions

ESD stan-dards

EARTh

Enipedia

Popula-tion (En-AKTing)

NHS(En-

AKTing) Mortality(En-

AKTing)

Energy (En-

AKTing)

Crime(En-

AKTing)

CO2 Emission

(En-AKTing)

EEA

SISVU

education.data.g

ov.uk

ECS South-ampton

ECCO-TCP

GND

Didactalia

DDC Deutsche Bio-

graphie

datadcs

MusicBrainz

(DBTune)

Magna-tune

John Peel

(DBTune)

Classical (DB

Tune)

AudioScrobbler (DBTune)

Last.FM artists

(DBTune)

DBTropes

Portu-guese

DBpedia

dbpedia lite

Greek DBpedia

DBpedia

data-open-ac-uk

SMCJournals

Pokedex

Airports

NASA (Data Incu-bator)

MusicBrainz(Data

Incubator)

Moseley Folk

Metoffice Weather Forecasts

Discogs (Data

Incubator)

Climbing

data.gov.uk intervals

Data Gov.ie

databnf.fr

Cornetto

reegle

Chronic-ling

America

Chem2Bio2RDF

Calames

businessdata.gov.

uk

Bricklink

Brazilian Poli-

ticians

BNB

UniSTS

UniPathway

UniParc

Taxonomy

UniProt(Bio2RDF)

SGD

Reactome

PubMedPub

Chem

PRO-SITE

ProDom

Pfam

PDB

OMIMMGI

KEGG Reaction

KEGG Pathway

KEGG Glycan

KEGG Enzyme

KEGG Drug

KEGG Com-pound

InterPro

HomoloGene

HGNC

Gene Ontology

GeneID

Affy-metrix

bible ontology

BibBase

FTS

BBC Wildlife Finder

BBC Program

mes BBC Music

Alpine Ski

Austria

LOCAH

Amster-dam

Museum

AGROVOC

AEMET

US Census (rdfabout)

Media

Geographic

Publications

Government

Cross-domain

Life sciences

User-generated content

Linking Open Data cloud diagram, by Richard Cyganiak and Anja Jentzsch. http://lod-cloud.net/

http://lod-cloud.net/


Outline




Reference Material


Classes and class hierarchy

Backbone of the ontology

AcademicStaff is a Class (A class will be interpreted as a set ofobjects)

AcademicStaff isa Staff (isa is interpreted as set inclusion)FacultyComponent

Course

MathCourse

ProbabilitiesAlgebra

LogicCSCourse

DBAIJava

Student

UndergraduateStudentMasterStudentPhDStudent

Department

PhysicsDeptMathsDeptCSDept

Staff

AcademicStaff

LecturerResearcherProfessor

AdministrativeStaff


Relations

Declaration of relations with their signature

(Relations will be interpreted as binary relations between objects)TeachesIn(AcademicStaff, Course)

if one states that “X TeachesIn Y ”, then X belongs toAcademicStaff and Y to Course

TeachesTo(AcademicStaff, Student)

Leads(Staff, Department)


Instances

Classes have instances

Dupond is an instance of the class Professor

corresponds to the fact: Professor(Dupond)

Relations also have instances

(Dupond,CS101) is an instance of the relation TeachesIn

corresponds to the fact: TeachesIn(Dupond,CS101)

The instance statements can be seen as (and stored in) a database


Ontology = schema + instance

Schema (TBox)

The set of class and relation namesThe signatures of relations and also constraintsThe constraints are used for two purposes

– checking data consistency (like dependencies in databases)– inferring new facts

Instance (ABox)

The set of factsThe set of base facts together with the inferred facts should satisfythe constraints

Ontology (i.e., Knowledge Base) = Schema + Instance


Outline

Introduction



Reference Material


3 ontology languages for the Web

RDF: a very simple ontology language

RDFS: Schema for RDF

Can be used to define richer ontologies

OWL: a much richer ontology language

We next present them rapidly


Outline

Introduction



Reference Material


Namespaces

An URI most often takes the form of a URL:http://live.dbpedia.org/page/%C3%89lectricit%C3%A9_de_Francehttp://sw.opencyc.org/2012/05/10/concept/en/GameOfChancehttp://www.w3.org/People/Berners-Lee/card#ihttp://www4.wiwiss.fu-berlin.de/dblp/resource/record/conf/www/2006

Some of these URIs may be actual URLs (point to a browsableresource), some may just be abstractFor simplicity, possibility of defining namespace prefixes, e.g.,dbpedia = http://live.dbpedia.org/page/ along with adefault prefix (e.g., mapped tohttp://sw.opencyc.org/2012/05/10/concept/en/):

dbpedia:%C3%89lectricit%C3%A9_de_France:GameOfChance

http://live.dbpedia.org/page/%C3%89lectricit%C3%A9_de_France

http://sw.opencyc.org/2012/05/10/concept/en/GameOfChance

http://www.w3.org/People/Berners-Lee/card#i

http://www4.wiwiss.fu-berlin.de/dblp/resource/record/conf/www/2006

http://www4.wiwiss.fu-berlin.de/dblp/resource/record/conf/www/2006

http://sw.opencyc.org/2012/05/10/concept/en/


RDF: Resource Description Framework

RDF facts are triplets

Each triplet is of the form: h Subject Predicate Object i

The subject is a URI, referencing an entity

The predicate is a URI, referencing a relation

The object is either a URI, referencing an entity, or a literalh :Dupond :Leads :CSDept ih :Dupond :HasName “Paul Dupond” ih :Dupond :TeachesIn :UE111 ih :Dupond :TeachesTo :Pierre ih :Pierre :EnrolledIn :CSDept ih :Pierre :RegisteredTo :UE111 ih :UE111 :OfferedBy :CSDept i

The linked data cloud contains dozens of billions of RDF triples


RDF graph

A set of RDF facts definesa set of relations between objectsan RDF graph where the nodes are objects:

:TeachesIn

:Dupond :Pierre

:InfoDept

UE111

:TeachesTo

:EnrolledIn

:RegisteredTo

:OfferedBy

:Leads


RDF semantics

A triplet hs P oi is interpreted in first-order logic (FOL) as a factP(s ; o)

Example:Leads(Dupond, CSDept)TeachesIn(Dupond, UE111)TeachesTo(Dupond,Pierre)EnrolledIn(Pierre, CSDept)RegisteredTo(Pierre, UE111)OfferedBy(UE111, CSDept)


RDF Serialization

Several serialization formats for RDF data, see alternate formats ofhttp://live.dbpedia.org/page/%C3%89lectricit%C3%A9_de_France:

RDF/XML, structured XML representation, allowing for nesting

N3 or Turtle, more compact, readable syntax, with some syntaxicsugar (Turtle is a subset of N3)

N-Triples, a simple text-based format

RDFa to integrate RDF annotations into HTML

http://live.dbpedia.org/page/%C3%89lectricit%C3%A9_de_France


Outline

Introduction



Reference Material


RDFS: RDF Schema

Not detailed here: the schema in RDF is super simplistic

An RDF Schema defines the schema of a richer ontology


RDF Schema

Do net get confused: RDFS can use RDF as syntax, i.e., RDFSstatements can be themselves expressed as RDF triplets usingsome specific properties and objects used as RDFS keywords witha particular meaning.

Declaration of classes and subclass relationshipsh Staff rdf:type rdfs:Class i

h Java rdfs:subClassOf CSCourse i

Declaration of instances (beyond the pure schema)h Dupond rdf:type AcademicStaff i


RDF Schema - continued

Declaration of relations (properties in RDFS terminology)

h RegisteredTo rdf:type rdfs:Property i

Declaration of subproperty relationships

h LateRegisteredTo rdfs:subPropertyOf RegisteredTo i

Declaration of domain and range restrictions for predicatesh TeachesIn rdfs:domain AcademicStaff i

h TeachesIn rdfs:range Course i

TeachesIn(AcademicStaff, Course)


RDFS logical semantics

RDF and RDFS statements FOL translation DL notationh i rdf:type C i C (i) i : C or C (i)h i P j i P(i ; j ) i P j or P(i ; j )h C rdfs:subClassOf D i 8X (C (X )) D(X )) C v Dh P rdfs:subPropertyOf R i 8X 8Y (P(X ;Y )) R(X ;Y )) P v Rh P rdfs:domain C i 8X 8Y (P(X ;Y )) C (X )) 9P v Ch P rdfs:range D i 8X 8Y (P(X ;Y )) D(Y )) 9P� v D

DL: Description logics, a specialized logical formalism


Outline

Introduction



Reference Material


OWL: Web Ontology Language

OWL extends RDFS with the possibility to express additionalconstraints

Main OWL constructs

Disjointness between classesConstraints of functionality and symmetry on predicatesIntentional class definitionsClass union and intersection

Corresponds to description logics


OWL constructs

Disjointness between classes:

OWL notation FOL translation DL notationh C owl:disjointWith D i 8X (C (X )) :D(X )) C v :D

Constraints of functionality and symmetry on predicates:OWL notation FOL translation DL notationh P rdf:typeowl:FunctionalProperty i

8X 8Y 8Z (funct P)

(P(X ;Y ) ^ P(X ;Z ) ) Y =

Z )

or 9P v (� 1P)

h P rdf:type 8X 8Y 8Z (funct P�)owl:InverseFunctionalProperty i (P(X ;Y ) ^ P(Z ;Y ) ) X =

Z )

or 9P� v (�

1P�)h P owl:inverseOf Q i 8X 8Y (P(X ;Y ) ,

Q(Y ;X ))

P � Q�

h P rdf:type owl:SymmetricPropertyi

8X 8Y (P(X ;Y ) )

P(Y ;X ))

P v P�


Definition of intentional classes in OWL

Goal: allow expressing complex constraints such as:departments can be lead only by professorsonly professors or lecturers may teach to undergraduate students.

The keyword owl:Restriction is used in association with a blanknode class, and some specific restriction properties:

owl:someValuesFromowl:allValuesFromowl:minCardinalityowl:maxCardinality


OWL Semantics

OWL notation FOL translation DL notation_a owl:onProperty P_a owl:allValuesFrom C 8Y (P(X ;Y )) C (Y )) 8P :C_a owl:onProperty P_a owl:someValuesFrom C 9Y (P(X ;Y ) ^C (Y )) 9P :C_a owl:onProperty P_a owl:minCardinality n 9Y1 : : : 9Yn(P(X ;Y1) ^ : : : ^

P(X ;Yn)^Vi ;j2[1::n ];i 6=j (Yi 6= Yj ))

(� n P)

_a owl:maxCardinality n 8Y1 : : : 8Yn8Yn+1

(P(X ;Y1) ^ : : : ^ P(X ;Yn) ^

P(X ;Yn+1)

(� n P)

)Wi ;j2[1::n+1];i 6=j (Yi = Yj ))


Unnamed new classes by example

Departments can be lead only by professors

Define the set of objects that are lead by professors_a rdfs:subClassOf owl:Restriction_a owl:onProperty Leads_a owl:allValuesFrom Professor

Now specify that all departments are lead by professorsDepartment rdfs:subClassOf _a


Union and Intersection of Classes byexample

Only professors or lecturers may teach to undergraduate students

_a rdfs:subClassOf owl:Restriction_a owl:onProperty TeachesTo_a owl:someValuesFrom Undergrad_b owl:unionOf (Professor, Lecturer)_a rdfs:subClassOf _b

This corresponds to an inclusion axiom in Description Logic:

9 TeachesTo.UndergraduateStudent v Professor t Lecturer

owl:equivalentClass corresponds to double inclusion:

MathStudent � Student u 9 RegisteredTo.MathCourse


Outline

Introduction



Reference Material


Querying using RDFS

RDFS statements can be used to infer new triples

Example

Base fact ResponsibleOf (durand ;ue111 )

Use the statement hResponsibleOf rdfs:domain Professorii.e., the logical rule: ResponsibleOf (X ;Y ) ) Professor(X )

With substitution {X/durand, Y/ue111}Infer fact Professor(durand)

Use the statement hProfessor rdfs:subClassOf AcademicStaff ii.e., the rule Professor(X ) ) AcademicStaff (X )

With substitution {X/durand}Infer fact AcademicStaff (durand)

etc.


The saturation algorithm

Keep infering new facts until a fixpoint is reached

Note: Only polynomially many facts can be added

ptime


Querying using DL

RDFS simpler and very used but limited

Query answering is unfeasible for all of OWL (even OWL-DL). . .but restrictions exist that have more reasonable complexity.


SPARQL: query language for RDF data

Graph pattern language

Get all URIs, name, emails of persons with all three pieces ofinformation from a FOAF dataset:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT *WHERE {

?person foaf:name ?name .?person foaf:mbox ?emails .

}

The SPARQL processor may or may not use reasoning w.r.t. theschema


Outline

Introduction



Reference Material


Where can Semantic Content be Found?

In the linked data, through Web-available RDF data:dumps of an entire ontology, in one of the RDF serializationformats (RDF/XML, Turtle, N-Triples)crawlable RDF content, with small fragments pointing to otherfragmentsa SPARQL endpointHTML annotated with RDFa,cf. http://www.w3.org/TR/rdfa-syntax/

Other popular semantic content embedded in Web pages:microformats (hCard, vCard, etc.), microdata(cf. http://www.schemas.org/). Not directly the spirit of theSemantic Web, but heavily used.

RDF content used internally in a company

http://www.w3.org/TR/rdfa-syntax/

http://www.schemas.org/


Systems

RDF stores (triplestores) with relational or native backend,open-source or commercial, seehttp://en.wikipedia.org/wiki/Triplestore. Apache Jena is apopular open-source Java store.

SPARQL engines, usually on top of a triplestore.http://en.wikipedia.org/wiki/SPARQL

Semantic browsers, to navigate RDF content,http://en.wikipedia.org/wiki/Linked_data#Browsers

A semantic Web search engine, http://sig.ma/

http://en.wikipedia.org/wiki/Triplestore

http://en.wikipedia.org/wiki/SPARQL

http://en.wikipedia.org/wiki/Linked_data#Browsers

http://sig.ma/


To go further. . .

The specifications on http://www.w3.org/

A gentle introduction to the Semantic Web:A Semantic Web Primer, G. Antoniou, F. van Harmelen, MITPress, 2008

A practical approach:Semantic Web for the Working Ontologist: Modeling in RDF,RDFS and OWL, Dean Allemang, James A. Hendler,Morgan-Kaufman, 2008

Contents of this lecture from:Web data management, S. Abiteboul, I. Manolescu, P. Rigaux,M.-C. Rousset, P. Senellart, Cambridge University Press, 2012.Also available at http://webdam.inria.fr/Jorge/

http://www.w3.org/

http://webdam.inria.fr/Jorge/

ontology languages - pierre senellart · 2012. 9. 7. · 3 / 43 télécom paristech pierre...

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