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Linked (Open) Data
INFO 4302 - April 18, 2011
Bernhard Haslhofer - Cornell University
Who am I?

• Postdoc at Cornell Information Science
• Research areas
 • linked data
 • user-contributed data (annotations)
 • (meta-)data interoperability
• Contact:
 • bernhard.haslhofer@cornell.edu
Today we talk about...



http://www.youtube.com/watch?v=5Cb3ik6zP2I
Today we talk about...

• Movies, actors and other real-world entities
• How to make data about these entities
 available on the Web (Linked Data)
• Enabling technologies, best-practices and
 useful tools that help us in doing so
• Other Linked Data projects (BBC, LoC)
Web Architecture Recap
The World Wide Web (WWW)
• Internet != WWW != Google != Facebook
• Fundamental technologies
 • URI - a simple and generic syntax for identifiers
 • HTML - a markup language without formal schema
     binding
 •   HTTP - a simple protocol to access and manipulate
     resources and resource representations in a
     distributed environment

• W3C Consortium (http://www.w3.org)
URIs

• Identification of resources via Uniform
  Resource Identifiers (URIs)
•The generic syntax consists of a hierarchical sequence of components, scheme,
  Generic Syntax:
 authority, path, query, and fragment.

 URI = scheme “:” hier-path [ “?” query ] [ “#” fragment ]

 Scheme and hier-path are required, though the path may be empty.

 Example URIs with components:                               URI


     foo://example.com:8042/over/there?name=ferret#nose
     _/ ________________/_________/ _________/ __/
                                        URL
      |           |             |            |       | URN
    scheme    authority        path        query   fragment
URIs / Resources

• Information Resource
 •   web pages, images, product catalogs, etc
 •   all their essential characteristics can be conveyed in a
     message
 •   e.g., http://www.flickr.com/user2/photos/image.jpg

• Non-Information Resource
 •   other things such as dogs, people, this classroom, concepts
 •   their essence is not information
 •   e.g., http://www.example.com/ontology/meter
HTTP


• A stateless request-response protocol in the
 client-server computing model
• HTTP methods: GET, POST, PUT, DELETE, ...
• Agents may use a URI to access the
 referenced resource = dereferencing the URI
HTTP Content Negotiation

• A URI is not (necessarily) a filename
• Conneg = making available multiple resource
 representations via the same URI

                                         Plain Text
                                         text/plain



                                         HTML (en)
                     URI                  text/html



                                         HTML (jp)
        http://example.com/The_Shining   text/html

                                         Resource
(X)HTML(5)
• A resource representation data format...
• ... for presentation markup
 • rendered by user agents (typically browsers)
 • focus on readability
 • less formal, user-friendly syntax and semantics
Web Services
• Application-to-application communication
 based on the Web architecture
 • simple and open standards (HTTP, XML, JSON, ...)
 • send data from Application A to Application B
     through the Web
 •   usually define some API



                          Web

         Application A               Application B
Linked Data
Why Linked Data?
Why Linked Data?
Why Linked Data?
Why Linked Data?

• There is lots of information on the Web
• ...valuable information that can be (re-)used
• Problem
 • information is usually expressed in the form of
     HTML documents
 •   the underlying raw data are locked in closed data
     silos (mostly DBMS)
(c) http://www.flickr.com/photos/docsearls/5500714140
Why Linked Data?

• The Web is successful because it provides
 • Uniform encoding (HTML)
 • Uniform addressing (URI)
 • Uniform transportation (HTTP)
 for the exchange of documents.
• Why not apply the same mechanism to the
 underlying data?
Linked (Open) Data
Linked (Open) Data
What is Linked Data?

• A method to build a Web of Data
• Architectural style, set of standards



                        Web
What is Linked Data?

• A set of four principles
 • use URIs as names for things
 • use HTTP URIs so that people can look up those
     names
 •   when someone looks up a URI, provide useful
     information, using the standards (RDF, SPARQL)
 •   include links to other URIs, so that they can
     discover more things
Enabling Technologies
Uniform Resource Identifiers (URI)

• Name and identify things (resources)
• Dereferencable HTTP URIs
                                   http://dbpedia.org/resource/
                                        The_Shining_(film)




      http://data.linkedmdb.org/
          resource/film/2014




                                   http://rdf.freebase.com/ns/m/
                                                 04fjzv
Resource Description Framework (RDF)

• A model for representing data on the Web
• Several statements (triples) form a graph
         http://dbpedia.org/ontology/                                                   http://xmlns.com/foaf/0.1/
                     Film                                                                         Person



                      rdf:type                                                                   rdf:type



         http://dbpedia.org/resource/                                                  http://dbpedia.org/resource/
                                                       dbpprop:starring
              The_Shining_(film)                                                               Jack_Nicholson



                                                                                                     foaf:name
              rdfs:label    rdfs:label
                                                                              dbpedia-owl:birthDate



    !" (#$)                        The Shining (film)                      1937-04-22                             Jack Nicholson
RDF serialization (RDF/XML, N3, Turtle, etc.)


• Data formats for RDF resource representations
   7.2.2.3            RDF Serialization Formats: RDF/XML, N3, Turtle, N-Triple, etc



• Used to transfer RDF data between apps
          Data formats for RDF resource representations

          Used to transfer RDF data from application-to-application

          N3/Turtle example:

         @prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
         @prefix dbpedia-owl:<http://dbpedia.org/ontology/> .

         <http://dbpedia.org/resource/The_Shining_%28film%29>
               rdf:type dbpedia-owl:Work , dbpedia-owl:Film .

         @prefix dbpprop:<http://dbpedia.org/property/> .
         @prefix ns9:<http://dbpedia.org/datatype/> .

         <http://dbpedia.org/resource/The_Shining_%28film%29>
               dbpprop:runtime"146.0"^^ns9:minute ;


   © Prof. Dr. Wolfgang Klas und Dr. Bernhard Haslhofer, WS 2010/11 - Multimediale Systeme 2
   7 Linked (Open) Data                                                                        7-15
RDF Vocabulary Description Language (RDFS)

• A language for describing the syntax and
 semantics of vocabularies in a machine-
 understandable way

                  http://dbpedia.org/ontology/
                             Work




                       rdfs:subClassOf




                  http://dbpedia.org/ontology/
                              Film
OWL - Web Ontology Language
• A more expressive (formal) language for defining the
  syntax and semantics of vocabularies
• Solves RDFS shortcomings but introduces quite some
  complexity

           http://www.w3.org/2002/07/                              http://dbpedia.org/ontology/
               owl#ObjectProperty                                             Work




                     rdf:type                        rdfs:domain




           http://dbpedia.org/ontology/                            http://dbpedia.org/ontology/
                                                     rdfs:range
                     starring                                                 Person



                            rdfs:label



                                          starring
Simple Knowledge Organization System (SKOS)

• A language for describing controlled vocabularies
      (taxonomies, thesauri, classification schemes)


                                              http://dbpedia.org/resource/
                                              Category:1980s_horror_films

                               skos:subject                                   rdf:type

http://dbpedia.org/resource/                         skos:broader
                                                                                         http://www.w3.org/2004/02/
     The_Shining_(film)                                                                       skos/core#Concept

                                                                             rdf:type
                                              http://dbpedia.org/resource/
                                                 Category:1980s_films
Links between Resources

   • OWL defines properties for linking resources
                             http://dbpedia.org/resource/                              http://dbpedia.org/resource/
                                                                 dbpprop:starring
                                  The_Shining_(film)                                           Jack_Nicholson



               owl:sameAs
                                                                                            owl:sameAs
                                          owl:sameAs
http://data.linkedmdb.org/
    resource/film/2014

                                                                                    http://data.nytimes.com/
                                                                                    N5761411277431266513
                                        http://rdf.freebase.com/ns/m/
                                                      04fjzv
SPARQL

 • A query language and protocol for accessing
7.2.2.7   SPARQL - RDF Query Language
    RDF data on the Web
    A query language and protocol for accessing RDF data on the Web


   SELECT DISTINCT ?x

   WHERE {?x skos:subject <http:dbpedia.org/resource/Cate-
      gory:1980s_horror_films>}

   LIMIT 10
Vocabulary / Data
Publishing Best Practices
Publishing Vocabularies
• Hash-based URIs
 •   e.g., http://example.com/example1#ClassA
 •   Suited to group the description of a moderate number of
     related terms into one RDF document
 •   Agent can retrieve terms with a single request

• Slash-based URIs
 •   e.g., http://example.com/example1/ClassB
 •   Suited to split terms in large vocabularies into one
     document per term
 •   No need to download a massive document
Provide either:

human-readable content from vocabulary URI
or:

machine-readable content from vocabulary URI




... depending on what is requested.
Linked (Open) Data
Linked (Open) Data
Publishing Data

• Distinguish between non-information and
 information resource
• Sample non-information resource
 • http://dbpedia.org/resource/The_Shining_(film)
• Sample information resource
 • http://dbpedia.org/page/The_Shining_(film) - HTML
 • http://dbpedia.org/data/The_Shining_(film) - RDF
Publishing Data

       GET http://dbpedia.org/resource/The_Shining_(film)
       Accept: application/rdf+xml



       303 See Other
       Location: http://dbpedia.org/data/The_Shining_(film)



       GET http://dbpedia.org/data/The_Shining_(film)
       Accept: application/rdf+xml



       200 OK
       ...
       <?xml version="1.0" encoding="utf-8"?>
       <rdf:RDF ...
The Linking Open Data
Community Project
Linking? Open? Data Project?

• Open Data: a philosophy, practice, or policy that data are
  freely available to everyone without restrictions from
  copyright, patents, a.s.o.

• Linked Data: method / best practices for exposing, sharing,
  and connecting data using URIs and RDF

• Linking Open Data: a W3C community project with the
  goal to extend the Web with a data commons by publishing
  various open data sets as RDF on the Web and by setting
  links between data items from different sources
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Linked (Open) Data
Useful Tools
RDF APIs
•   Java
    •   Jena Semantic Web Framework (http://openjena.org/)
    •   Sesame RDF API (http://www.openrdf.org/)

•   PHP
    •   ARC (http://arc.semsol.org/)

•   Ruby
    •   RDF.rb: Linked Data for Ruby (http://rdf.rubyforge.org/)

•   Python
    •   RDFLib (http://www.rdflib.net/)

•   C
    •   Redland RDF Libraries (http://librdf.org/)
RDF Stores

• OpenLink Virtuoso (http://virtuoso.openlinksw.com/
  dataspace/dav/wiki/Main/)
• 4Store (http://4store.org/)
• AllegroGraph (http://www.franz.com/agraph/
  allegrograph/)
• Oracle 11g (http://www.oracle.com/technetwork/
  database/options/semantic-tech/ index.html)
• ...and many more: http://www.w3.org/2001/sw/wiki/Tools
RDF / Linked Data Wrappers
• D2RQ - SPARQL / Linked Data for relational
 databases (http://www4.wiwiss.fu-berlin.de/
 bizer/d2rq/)
• OAI2LOD Server - expose any OAI-PMH
 source as Linked Data
• TripFS - filesystem as Linked Data
• TripCel - XLS spreadsheets as Linked Dat
• ...
Linked Data debugging

Startup your console / terminal
  - native on Linux / Mac OS X
  - Windows: http://www.cygwin.com/

Dereference resources with cURL (http://curl.haxx.se/)
curl -I -H "Accept: application/rdf+xml" http://
dbpedia.org/resource/The_Shining_%28film%29

curl -H "Accept: application/rdf+xml" http://
dbpedia.org/data/The_Shining_%28film%29
Linked Data debugging

Install the Raptor RDF Syntax Library (http://
librdf.org/raptor/)
  - Mac: brew install raptor

Use the rapper utility to dereference URIs
rapper http://dbpedia.org/resource/The_Shining_%28film
%29

rapper -o rdfxml http://dbpedia.org/resource/
The_Shining_%28film%29
Readings
Required Reading



• T. Heath, C. Bizer. Linked Data: Evolving the Web into a
  Global Data Space, Chapters 1-5

  http://linkeddatabook.com/editions/1.0/
Recommended Readings
• Linked Data Web Site: http://linkeddata.org
• Linked Data / Semantic Web Introduction: http://
  www.linkeddatatools.com/semantic-web-basics
• Tim Berners-Lee. Linked Data Design Issues: http://
  www.w3.org/DesignIssues/LinkedData.html
• Best Practice Recipes for Publishing RDF Vocabularies:
  http://www.w3.org/TR/swbp-vocab-pub/
• How to Publish Linked Data on the Web: http://
  www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/

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Linked (Open) Data

  • 1. Linked (Open) Data INFO 4302 - April 18, 2011 Bernhard Haslhofer - Cornell University
  • 2. Who am I? • Postdoc at Cornell Information Science • Research areas • linked data • user-contributed data (annotations) • (meta-)data interoperability • Contact: • bernhard.haslhofer@cornell.edu
  • 3. Today we talk about... http://www.youtube.com/watch?v=5Cb3ik6zP2I
  • 4. Today we talk about... • Movies, actors and other real-world entities • How to make data about these entities available on the Web (Linked Data) • Enabling technologies, best-practices and useful tools that help us in doing so • Other Linked Data projects (BBC, LoC)
  • 6. The World Wide Web (WWW) • Internet != WWW != Google != Facebook • Fundamental technologies • URI - a simple and generic syntax for identifiers • HTML - a markup language without formal schema binding • HTTP - a simple protocol to access and manipulate resources and resource representations in a distributed environment • W3C Consortium (http://www.w3.org)
  • 7. URIs • Identification of resources via Uniform Resource Identifiers (URIs) •The generic syntax consists of a hierarchical sequence of components, scheme, Generic Syntax: authority, path, query, and fragment. URI = scheme “:” hier-path [ “?” query ] [ “#” fragment ] Scheme and hier-path are required, though the path may be empty. Example URIs with components: URI foo://example.com:8042/over/there?name=ferret#nose _/ ________________/_________/ _________/ __/ URL | | | | | URN scheme authority path query fragment
  • 8. URIs / Resources • Information Resource • web pages, images, product catalogs, etc • all their essential characteristics can be conveyed in a message • e.g., http://www.flickr.com/user2/photos/image.jpg • Non-Information Resource • other things such as dogs, people, this classroom, concepts • their essence is not information • e.g., http://www.example.com/ontology/meter
  • 9. HTTP • A stateless request-response protocol in the client-server computing model • HTTP methods: GET, POST, PUT, DELETE, ... • Agents may use a URI to access the referenced resource = dereferencing the URI
  • 10. HTTP Content Negotiation • A URI is not (necessarily) a filename • Conneg = making available multiple resource representations via the same URI Plain Text text/plain HTML (en) URI text/html HTML (jp) http://example.com/The_Shining text/html Resource
  • 11. (X)HTML(5) • A resource representation data format... • ... for presentation markup • rendered by user agents (typically browsers) • focus on readability • less formal, user-friendly syntax and semantics
  • 12. Web Services • Application-to-application communication based on the Web architecture • simple and open standards (HTTP, XML, JSON, ...) • send data from Application A to Application B through the Web • usually define some API Web Application A Application B
  • 17. Why Linked Data? • There is lots of information on the Web • ...valuable information that can be (re-)used • Problem • information is usually expressed in the form of HTML documents • the underlying raw data are locked in closed data silos (mostly DBMS)
  • 19. Why Linked Data? • The Web is successful because it provides • Uniform encoding (HTML) • Uniform addressing (URI) • Uniform transportation (HTTP) for the exchange of documents. • Why not apply the same mechanism to the underlying data?
  • 22. What is Linked Data? • A method to build a Web of Data • Architectural style, set of standards Web
  • 23. What is Linked Data? • A set of four principles • use URIs as names for things • use HTTP URIs so that people can look up those names • when someone looks up a URI, provide useful information, using the standards (RDF, SPARQL) • include links to other URIs, so that they can discover more things
  • 25. Uniform Resource Identifiers (URI) • Name and identify things (resources) • Dereferencable HTTP URIs http://dbpedia.org/resource/ The_Shining_(film) http://data.linkedmdb.org/ resource/film/2014 http://rdf.freebase.com/ns/m/ 04fjzv
  • 26. Resource Description Framework (RDF) • A model for representing data on the Web • Several statements (triples) form a graph http://dbpedia.org/ontology/ http://xmlns.com/foaf/0.1/ Film Person rdf:type rdf:type http://dbpedia.org/resource/ http://dbpedia.org/resource/ dbpprop:starring The_Shining_(film) Jack_Nicholson foaf:name rdfs:label rdfs:label dbpedia-owl:birthDate !" (#$) The Shining (film) 1937-04-22 Jack Nicholson
  • 27. RDF serialization (RDF/XML, N3, Turtle, etc.) • Data formats for RDF resource representations 7.2.2.3 RDF Serialization Formats: RDF/XML, N3, Turtle, N-Triple, etc • Used to transfer RDF data between apps Data formats for RDF resource representations Used to transfer RDF data from application-to-application N3/Turtle example: @prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix dbpedia-owl:<http://dbpedia.org/ontology/> . <http://dbpedia.org/resource/The_Shining_%28film%29> rdf:type dbpedia-owl:Work , dbpedia-owl:Film . @prefix dbpprop:<http://dbpedia.org/property/> . @prefix ns9:<http://dbpedia.org/datatype/> . <http://dbpedia.org/resource/The_Shining_%28film%29> dbpprop:runtime"146.0"^^ns9:minute ; © Prof. Dr. Wolfgang Klas und Dr. Bernhard Haslhofer, WS 2010/11 - Multimediale Systeme 2 7 Linked (Open) Data 7-15
  • 28. RDF Vocabulary Description Language (RDFS) • A language for describing the syntax and semantics of vocabularies in a machine- understandable way http://dbpedia.org/ontology/ Work rdfs:subClassOf http://dbpedia.org/ontology/ Film
  • 29. OWL - Web Ontology Language • A more expressive (formal) language for defining the syntax and semantics of vocabularies • Solves RDFS shortcomings but introduces quite some complexity http://www.w3.org/2002/07/ http://dbpedia.org/ontology/ owl#ObjectProperty Work rdf:type rdfs:domain http://dbpedia.org/ontology/ http://dbpedia.org/ontology/ rdfs:range starring Person rdfs:label starring
  • 30. Simple Knowledge Organization System (SKOS) • A language for describing controlled vocabularies (taxonomies, thesauri, classification schemes) http://dbpedia.org/resource/ Category:1980s_horror_films skos:subject rdf:type http://dbpedia.org/resource/ skos:broader http://www.w3.org/2004/02/ The_Shining_(film) skos/core#Concept rdf:type http://dbpedia.org/resource/ Category:1980s_films
  • 31. Links between Resources • OWL defines properties for linking resources http://dbpedia.org/resource/ http://dbpedia.org/resource/ dbpprop:starring The_Shining_(film) Jack_Nicholson owl:sameAs owl:sameAs owl:sameAs http://data.linkedmdb.org/ resource/film/2014 http://data.nytimes.com/ N5761411277431266513 http://rdf.freebase.com/ns/m/ 04fjzv
  • 32. SPARQL • A query language and protocol for accessing 7.2.2.7 SPARQL - RDF Query Language RDF data on the Web A query language and protocol for accessing RDF data on the Web SELECT DISTINCT ?x WHERE {?x skos:subject <http:dbpedia.org/resource/Cate- gory:1980s_horror_films>} LIMIT 10
  • 34. Publishing Vocabularies • Hash-based URIs • e.g., http://example.com/example1#ClassA • Suited to group the description of a moderate number of related terms into one RDF document • Agent can retrieve terms with a single request • Slash-based URIs • e.g., http://example.com/example1/ClassB • Suited to split terms in large vocabularies into one document per term • No need to download a massive document
  • 36. or: machine-readable content from vocabulary URI ... depending on what is requested.
  • 39. Publishing Data • Distinguish between non-information and information resource • Sample non-information resource • http://dbpedia.org/resource/The_Shining_(film) • Sample information resource • http://dbpedia.org/page/The_Shining_(film) - HTML • http://dbpedia.org/data/The_Shining_(film) - RDF
  • 40. Publishing Data GET http://dbpedia.org/resource/The_Shining_(film) Accept: application/rdf+xml 303 See Other Location: http://dbpedia.org/data/The_Shining_(film) GET http://dbpedia.org/data/The_Shining_(film) Accept: application/rdf+xml 200 OK ... <?xml version="1.0" encoding="utf-8"?> <rdf:RDF ...
  • 41. The Linking Open Data Community Project
  • 42. Linking? Open? Data Project? • Open Data: a philosophy, practice, or policy that data are freely available to everyone without restrictions from copyright, patents, a.s.o. • Linked Data: method / best practices for exposing, sharing, and connecting data using URIs and RDF • Linking Open Data: a W3C community project with the goal to extend the Web with a data commons by publishing various open data sets as RDF on the Web and by setting links between data items from different sources
  • 57. RDF APIs • Java • Jena Semantic Web Framework (http://openjena.org/) • Sesame RDF API (http://www.openrdf.org/) • PHP • ARC (http://arc.semsol.org/) • Ruby • RDF.rb: Linked Data for Ruby (http://rdf.rubyforge.org/) • Python • RDFLib (http://www.rdflib.net/) • C • Redland RDF Libraries (http://librdf.org/)
  • 58. RDF Stores • OpenLink Virtuoso (http://virtuoso.openlinksw.com/ dataspace/dav/wiki/Main/) • 4Store (http://4store.org/) • AllegroGraph (http://www.franz.com/agraph/ allegrograph/) • Oracle 11g (http://www.oracle.com/technetwork/ database/options/semantic-tech/ index.html) • ...and many more: http://www.w3.org/2001/sw/wiki/Tools
  • 59. RDF / Linked Data Wrappers • D2RQ - SPARQL / Linked Data for relational databases (http://www4.wiwiss.fu-berlin.de/ bizer/d2rq/) • OAI2LOD Server - expose any OAI-PMH source as Linked Data • TripFS - filesystem as Linked Data • TripCel - XLS spreadsheets as Linked Dat • ...
  • 60. Linked Data debugging Startup your console / terminal - native on Linux / Mac OS X - Windows: http://www.cygwin.com/ Dereference resources with cURL (http://curl.haxx.se/) curl -I -H "Accept: application/rdf+xml" http:// dbpedia.org/resource/The_Shining_%28film%29 curl -H "Accept: application/rdf+xml" http:// dbpedia.org/data/The_Shining_%28film%29
  • 61. Linked Data debugging Install the Raptor RDF Syntax Library (http:// librdf.org/raptor/) - Mac: brew install raptor Use the rapper utility to dereference URIs rapper http://dbpedia.org/resource/The_Shining_%28film %29 rapper -o rdfxml http://dbpedia.org/resource/ The_Shining_%28film%29
  • 63. Required Reading • T. Heath, C. Bizer. Linked Data: Evolving the Web into a Global Data Space, Chapters 1-5 http://linkeddatabook.com/editions/1.0/
  • 64. Recommended Readings • Linked Data Web Site: http://linkeddata.org • Linked Data / Semantic Web Introduction: http:// www.linkeddatatools.com/semantic-web-basics • Tim Berners-Lee. Linked Data Design Issues: http:// www.w3.org/DesignIssues/LinkedData.html • Best Practice Recipes for Publishing RDF Vocabularies: http://www.w3.org/TR/swbp-vocab-pub/ • How to Publish Linked Data on the Web: http:// www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/