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Semantic WebIntroduction to semantic data
Catherine Comparot Nathalie Hernandez Cassia Trojahn
UT2J - IRIT, MELODI Team
7th June, 2016
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Agenda
Why the Semantic Web ?
Semantic data on the Linked Open Data
One step further : the Semantic Web
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Agenda
Why the Semantic Web ?Artificial IntelligenceThe syntactic webLimits of the syntactic Web
Semantic data on the Linked Open Data
One step further : the Semantic Web
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Artificial Intelligence
A definition, proposed by J. Pitrat
”Artificial Intelligence is the science which aims is to makemachines do what humans are capable of doing.”
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Levels of ”understanding”
I Data : Result of a measure
I Information : Data and its context
I Knowledge : Possible deductions from information withbackground rules (reasoning)
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Levels of ”understanding”
I Data : Result of a measure
I Information : Data and its context
I Knowledge : Possible deductions from information withbackground rules (reasoning)
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Levels of ”understanding”
I Data : Result of a measure
I Information : Data and its context
I Knowledge : Possible deductions from information withbackground rules (reasoning)
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Levels of ”understanding”
I Data : Result of a measure
I Information : Data and its context
I Knowledge : Possible deductions from information withbackground rules (reasoning)
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Levels of ”understanding”
I Data : Result of a measure
I Information : Data and its context
I Knowledge : Possible deductions from information withbackground rules (reasoning)
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Logic
Logic models formalize common sense andreasoning mechanisms in order to studyand automatize them.
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What is a logic ?
Constituents of a logic
I A syntax (grammar + vocabulary)
I A semantic
I A mechanism for deduction
Their roles (respectively)
I Describe data
I Associate meaning to the data
I Deduce new knowledge
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Internet and the Web
InternetNetwork of computers offering countless services
The WebThe World Wide Web is an information systemsupported by Internet based on :
I a system addressing the resources (page,image, video) via their URL
I HTML pages related thanks to hyperlinks
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The W3C
A organism standardizing the web
Founded in 1993 by Tim Berners Lee
What does the W3C standardize?
I Web Application (HTML, CSS, Ajax...)
I Web Architectures (URL, HTTP...)
I XML & consorts (XPath, ...)
I Web Services (SOAP, WSDL)
I Semantic Web languages (RDF, OWL, ..)
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
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What you can do with the Web...
I Search for plane tickets to go toVenice
I Adapt the dates according to forecastI Avoid rainy days until I receive the
boots that I’ve orderedI Take into consideration my medical
constraints
I Book a room in the Hotel where G.Clooney stayed
I Command a pizza without gluten anda Torus bottle to cheer me up as noroom is available at the suitabledates...
... if you know where to look ...
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What you do not want to do...
:(
I Use complicated tools
I Search in several sources
I Go further than the first google page of results ...
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Any semantics in this Web to help?
What humans see
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Any semantics in this Web to help?
What computers see ...
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Any semantics in this Web to help?
What computers see?
More syntax than dogs thanks to HTML !
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Any semantics in this Web to help?
Limitations of HTML markups
I HTML markups are defined by web page authors and notpeople looking for information
I Markups indicate information ”zones” and links betweenresources
I No formal semantic or common sense associated to thesezones or links
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Any semantics in this Web to help?
The data used in Geosciences
I data distributed in several sources
I data in different formats
I a considerable effort to use (extract, combine, ...) them forspecific applications
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Semantics please HELP US!
The founder article of the Semantic Web
I Tim Berners Lee, at the conference WWW in 1994http://www.w3.org/Talks/WWW94Tim/
I The Semantic Web is a new form of the syntactic Web inwhich content is meaningful to computers and humansthus unleashing a revolution of new possibilities
I The Semantic Web relies on standards allowing torepresent knowledge usable by computers.
I Today’s reality : the Linked Open Data (LOD)
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Agenda
Why the Semantic Web ?
Semantic data on the Linked Open DataData semantizationLinked Open Data cloud
One step further : the Semantic Web
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Sacre Tim !
From 1 To 5 stars data !Tim Berners Lee (him again!!!) has proposed a hierarchisation ofdata which reflects their quality in the perspective of making themopen and reusable.
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One star data
data characteristics
I Data accessible on the Web, with an open license.For example, the following pdf document :
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Two star data
data characteristics
I data in a structured format.For example, the same table but in the xls format.
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Three star data
data characteristics
I data in an open format.For example, the same table in csv.
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Four star data
data characteristics
I data described with RDF (a W3C formalism!)
I First step towards semantic description of data !!!For example, the same table in RDF.
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The RDF, graph language
Bases of RDF : the triplet
I A triplet is composed of 3 resources :I The subject : the resource the representation is talking aboutI The predicate : the property of the subjectI The object : who/what the property links the subject to
What RDF adds
I Resources can be physical documents (web pages, video...),”moral” resources (person, institution, color,...) or data value
I The predicate makes explicit the nature of the link betweenresources
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The RDF, graph language
Bases of RDF : the triplet
I A triplet is composed of 3 resources :I The subject : the resource the representation is talking aboutI The predicate : the property of the subjectI The object : who/what the property links the subject to
What RDF adds
I Resources can be physical documents (web pages, video...),”moral” resources (person, institution, color,...) or data value
I The predicate makes explicit the nature of the link betweenresources
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The IRI
I Unique identification of resources on the Web
I Evolution of the notion of URL for internationalizationI Examples :
I IRI of an observation :http://pelican/adreamdataCNRS.RDC.EXT.LUX.mesure 01/03/2015%2000
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Examples of RDF triplets
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Five star data
data characteristics
I data linked to data from other data sets
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The Linked Open Data cloud
Where are we now ?
I Who? A lot of people on the LOD : BBC, MusicBrainz,Wikipedia, IBM, IEEE, flickr, etc...
I What? Everything : 5 star data dealing with music, science,geography, government, ...
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Agenda
Why the Semantic Web ?
Semantic data on the Linked Open Data
One step further : the Semantic WebInterrogation de donnees liees : SPARQLOntologyReasoning
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More semantics thanks to W3C standards !
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Querying RDF data with SPARQL
What is SPARQL ?
I Retrieves, deletes, updates RDF graphs
I Works by indicating graph patterns
I Syntax similar to SQL
I Not suited for end-users...
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Example of SPARQL query
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What is an ontology ?
An academic definitionAn ontology is a formal, and explicit specification of a sharedconceptualisation [Studer, 1998]
More concretely
An ontology is a shared and formalized vocabulary used to describedata or information to
I enable interoperability
I infer new knowledge
An ontology is a knowledge representation used by agents(computers).
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What is an ontology ?
What do we have in an ontology?
I Labels (lexicon or symbols) : fog, nieba
I Classes (notions, set of objects, event, state,...): Sensor,Location, City, Observation...
I Relations between classes
I Hierarchy of classes: City is a LocationI Properties: Sensor observes parameter, Observation occurs in
Location, ...
I More axioms : A sensor that observes a Temperature is aTemperatureSensor
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What is an ontology ?
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Description logic
The OWL language for representing ontologies
I a W3C formalism
I relies on Description Logics (DL)
Two types of axioms in DL
I Terminological (T-box) : defining the vocabularyI ssn : Sensor v ssn : DeviceI ssn : Sensor u ssn : Actuator v⊥I ssn : LightSensor ≡ ssn : Sensor u ∃ssn : observes.qudt : Light
I Assertional (A-box) : asserting facts on data with thevocabulary (or data semantic description)
I XXX ∈ ssn : Sensor
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How is the formalization exploited ?
The reasoner
I is a program which uses the vocabulary, the logic in which it isrepresented and the assertions made on data to infer newfacts.
I can detect inconsistencies when logical rules are violated.
An inference
I corresponds to a new fact deduced by the reasoner
I relies on different characterics of the used logic
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Inference based on properties
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Inference based on properties
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Inference based on the hierarchy of classes
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Inference based on class definition
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Inference based on class definition
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Inference based on class definition
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Different levels of formalization
Type Content LanguageLightweight ontology Class hierarchy and properties RDFSHeavyweight ontology Lightweight ontology - More axioms OWL
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Different ”roles” for ontologies
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Ontology Alignment
Alignment
I Finding corresponding entities between ontologies orknowledge bases
I The possible links :I Equivalence/DisjointednessI Specialization/Generalization/Composition
I A branch of Semantic Web is dedicated to the study ofautomated ways for generating alignments
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Example of Alignment
SSN and SAREF : T-box Alignments
I saref:Device ≡ ssn:Device
I ssn:startTime ⊂ saref:Time
I saref:UnitOfMeasure ⊂ ssn:MeasuringCapability
A-box Alignment
I Toulouse : http://sws.geonames.org/2972315 ≡http://fr.dbpedia.org/resource/Toulouse
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Alignment and reasoning
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Alignment and reasoning
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Alignment and reasoning
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The semantic Web for GeoScienceA project using ontologies for both interoperability andreasoning
http://citydata.ai.wu.ac.at/
KPIDataPipeline/
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