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Usage of Linked Data: Introduction and Application Scenarios

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This presentation introduces the main principles of Linked Data, the underlying technologies and background standards. It provides basic knowledge for how data can be published over the Web, how it can be queried, and what are the possible use cases and benefits. As an example, we use the development of a music portal (based on the MusicBrainz dataset), which facilitates access to a wide range of information and multimedia resources relating to music.

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Usage of Linked Data: Introduction and Application Scenarios

  1. 1. Usage of Linked DataIntroduction and Application ScenariosPresented by:Barry Norton
  2. 2. Agenda1. Motivation Scenario2. Linked Data Foundations3. Introduction to Linked Data4. Linked Data use case scenarios2
  4. 4. Music!4• Provision of a music-based portal.• Bring together a number of disparate components ofdata-oriented content:1. Musical content (streaming data & downloads)2. Music and artist metadata3. Review content4. Visual content (pictures of artists & albums)
  5. 5. Music!5VisualizationModuleMetadataStreaming providersPhysical WrapperDownloadsDataacquisitionD2R Transf.LD WrapperMusical ContentApplicationAnalysis &Mining ModuleLDDatasetAccessLD WrapperRDF/XMLIntegratedDatasetInterlinking CleansingVocabularyMappingSPARQLEndpointPublishingRDFaOther content
  6. 6. Music!6Expected Results• The developer will contribute back the aggregated andinterlinked content to the Linked Open Data Cloud.• Linking of artists will be improved.• Metadata, visual content and reviews will be improved.• Links to emerging Web technologies that inherit fromsemantics: Google RichSnippets, Facebook OpenGraphand annotation.
  8. 8. • Extension of the technology of computernetworks.• The technology supporting the Internetincludes the Internet Protocol (IP) .• Each computer on the Internet is assigned anIP number.• Messages can be routed from one computerto another.Internet8
  9. 9. Internet9Source: http://www.evolutionoftheweb.comThe growth of the Internet
  10. 10. • There is a wealth of information on the Web.• It is aimed mostly towards consumption byhumans as end-users:• Recognize the meaning behind content and draw conclusions,• Infer new knowledge using context and• Understand background information.TheWeb10
  11. 11. TheWeb11• Billions of diverse documents online, but it is not easilypossible to automatically:• Retrieve relevant documents.• Extract information.• Combine information in a meaningful way.• Idea:• Also publish machine processable data on the web.• Formulate questions in terms understandable for a machine.• Do this in a standardized way so machines can interoperate.• The Web becomes a Web of Data• This provides a common framework to share knowledge on the Webacross application boundaries.
  12. 12. TheWeb: Evolution12Web of Documents Web of Data"Documents"Hyperlinks Typed Links"Things"
  13. 13. TheWeb: Evolution13Source:
  14. 14. WebTechnology Basics14HTML – HyperText Markup Language• Language for displaying web pages and otherinformation in a web browser.• HTML elements consist of tags (enclosed in anglebrackets), attributes and content.HTTP – HypertextTransfer Protocol• Foundation of data communication for the WWW.• Client-server protocol.• Every interaction is based on: request and response.
  15. 15. WebTechnology Basics15Uniform Resource Identifier (URI)• Compact sequence of characters that identifies anabstract or physical resource.• Examples:ldap://[2001:db8::7]/c=GB?objectClass?onemailto:John.Doe@example.comnews:comp.infosystems.www.servers.unixtel:+1-816-555-1212telnet://
  16. 16. Describing Data16Vocabularies• Collections of defined relationships and classes ofresources.• Classes group together similar resources.• Terms from well-known vocabularies should bereused wherever possible.• New terms should be define only if you can not findrequired terms in existing vocabularies.
  17. 17. Describing Data17VocabulariesA set of well-known vocabularies has evolved in theSemantic Web community. Some of them are:Vocabulary Description Classes and RelationshipsFriend-of-a-Friend (FOAF) Vocabulary for describingpeople.foaf:Person, foaf:Agent, foaf:name,foaf:knows, foaf:memberDublin Core (DC) Defines general metadataattributes.dc:FileFormat, dc:MediaType,dc:creator, dc:descriptionSemantically-InterlinkedOnline Communities (SIOC)Vocabulary for representingonline communities.sioc:Community, sioc:Forum,sioc:Post, sioc:follows, sioc:topicMusic Ontology (MO) Provides terms for describingartists, albums and, mo:MusicGroup,mo:Signal, mo:member, mo:recordSimple KnowledgeOrganization System (SKOS)Vocabulary for representingtaxonomies and looselystructured knowledge.skos:Concept, skos:inScheme,skos:definition, skos:example
  18. 18. Describing Data18VocabulariesMore extensive lists of well-known vocabularies aremaintained by:• W3C SWEO Linking Open Data community project• Mondeca: Linked Open Vocabularies• Library Linked Data Incubator Group: Vocabularies inthe library domain
  19. 19. Semantics on theWeb19Semantic Web StackBerners-Lee (2006)
  20. 20. Semantics on theWeb20Semantic Web StackBerners-Lee (2006)Syntatic basisBasic data modelSimple vocabulary(schema) languageExpressive vocabulary(ontology) languageQuery languageApplication specificdeclarative-knowledgeDigital signatures,recommendationsProof generation,exchange, validation
  21. 21. Semantics on theWeb21Semantic Web StackBerners-Lee (2006)RDF – Resource Description Framework
  22. 22. Semantics on theWeb22RDF – Resource Description Framework• RDF is the basis layer of the Semantic Web stack‘layer cake’.• Basic building block: RDF triple.• Subject – a resource, which may be identified with a URI.• Predicate – a URI-identified reused specification of therelationship.• Object – a resource or literal to which the subject is related.
  23. 23. Semantics on theWeb23RDF – Resource Description Framework(Example)<><><>.<><>"The Beatles" .URIs are given inangle brackets inN-Triples.Literals are given in quotes in N-Triples.In N-Triples everystatement isterminated with afull stop.
  24. 24. Semantics on theWeb24RDF Graphs• Every set of RDF assertions can then be drawn andmanipulated as a (labelled directed) graph:• Resources – the subjects and objects are nodes of thegraph.• Predicates – each predicate use becomes a label for an arc,connecting the subject to the object.Subject ObjectPredicate
  25. 25. RDF Graphs (Example)25<><><><> "The Beatles"Semantics on theWeb
  26. 26. Semantics on theWeb26RDF Blank Nodes• RDF graphs can also contain unidentified resources, calledblank nodes:• Blank nodes can group related information, but their use inLinked Data is discouraged.[] <><><><>49.005 8.386
  27. 27. Semantics on theWeb27RDFTurtle• Turtle is a syntax for RDF more readable.• Since many URIs share same basis we use prefixes:@prefix rdf:<>.@prefix rdfs:<>.@prefix owl:<>.@prefix mo:<>.@prefix dbpedia:<>.And (sometimes) a unique base:@base <>.
  28. 28. Semantics on theWeb28RDFTurtle• Also has a simple shorthand for class membership:@base <>.@prefix mo:<>.<artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_> a mo:MusicGroup.Is equivalent to:<><><>.
  29. 29. RDFTurtle• When multiple statements apply to same subject theycan be abbreviated as follows:<artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_>rdfs:label "The Beatles";owl:sameAs dbpedia:The_Beatles ,<> .Same subject &predicateSemantics on theWeb29Same subject
  30. 30. RDFTurtle• Turtle also provides a simple syntax for datatypes andlanguage tags for literals, respectively:<recording/5098d0a8-d3c3-424e-9367-1f2610724410#_> a mo:Signal;rdfs:label "All You Need Is Love" ;mo:duration "PT3M48S"^^xsd:duration .dbpedia:The_Beatles dbpedia-owl:abstract"The Beatles were an English rock band formed (…) "@en,"The Beatles waren eine britische Rockband in den (…) "@de .Semantics on theWeb30
  31. 31. Semantics on theWeb31RDF/XML• This is most useful for inter-machine communication.• The primary (recurring) element in encodingassertions (thereby triples) is rdf:Description, e.g.:<rdf:Descriptionrdf:about=""><foaf:name>The Beatles</foaf:name><owl:sameAs rdf:resource=""></rdf:Description><rdf:Descriptionrdf:about=""><foaf:name>John Lennon</foaf:name></rdf:Description>
  32. 32. Semantics on theWeb32Semantic Web StackBerners-Lee (2006)RDF-S – RDF Schema
  33. 33. Semantics on theWeb33RDF-S – RDF SchemaLanguage for two tasks w.r.t. the RDF data model:• Expectation – nominate:• the ‘types’, i.e., classes, of things we might makeassertions about, and• the properties we might apply, as predicates in theseassertions, to capture their relationships.• Inference – given a set of assertions, using these classesand properties, specify what should be inferred aboutassertions that are implicitly made.
  34. 34. Semantics on theWeb34RDF-S – RDF Schema• rdf:Property - Class of RDF properties. Example:mo:member - Indicates a member of a musical group.• rdfs:domain - States that any resource that has a givenproperty is an instance of one or more rdfs:domain mo:MusicGroup .• rdfs:range - States that the values of a property areinstances of one or more rdfs:range foaf:Agent .
  35. 35. Semantics on theWeb35RDF-S – RDF Schemamo:MusicGrouprdfs:subClassOffoaf:Group .<artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_>rdf:typemo:MusicGroup .<artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_>rdf:typefoaf:Group .SchemaExistingfactInferredfactWe expect to use thisvocabulary to make assertionsabout music groups.Having made such anassertion...Inferences can be drawn thatwe did not explicitly make
  36. 36. Semantics on theWeb36RDF-S – RDF SchemaResources and predicateswith (limited) inferences:rdfs:Resourcerdfs:Literal, rdfs:Datatyperdfs:Class, rdfs:subClassOfrdfs:subPropertyOfrdfs:range, rdfs:domainSome predicates withNO inferences:rdfs:commentrdfs:labelrdfs:seeAlsordfs:isDefinedByrdf:Property (an instance of rdfs:Class)
  37. 37. Semantics on theWeb37Semantic Web StackBerners-Lee (2006)OWL – Web Ontology Language
  38. 38. Semantics on theWeb38OWL – Web Ontology Language• RDFS provides a simplified ontological language fordefining vocabularies about specific domains.• Sometimes it is necessary to have access to a widerrange of ontological constructs.• Web Ontology Language (OWL) provides moreontological constructs and avoids some of thepotential confusion in RDF-S.
  39. 39. Semantics on theWeb39OWL 2.0 – Web Ontology Language 2.0Extends the DL further, but has three more computable fragments(profiles). OWL 2 Full• Used informally to refer to RDF graphs consideredas OWL 2 ontologies and interpreted using theRDF-Based Semantics.OWL 2 DL• Used informally to refer to OWL 2 DL ontologiesinterpreted using the Direct Semantics.OWL 2 EL• Limited to basic classification, but withpolynomial-time reasoning.OWL 2 QL• Designed to be translatable to relational databasequerying.OWL 2 RL• Designed to be efficiently implementable in rule-based systems.OWL 2 FullOWL 2 DLOWL 2 ELOWL 2 QL OWL 2 RL
  40. 40. Semantics on theWeb40OWL – Web Ontology LanguageOWL is made up of terms which provide for:• Class construction: forming new classes from membership of existingones (e.g., unionOf, intersectionOf, etc.).• Property construction: distinction between OWL ObjectProperties(resources as values) and OWL DatatypeProperties (literals as values).• Class axioms: sub-class, equivalence and disjointness relationships.• Property axioms: sub-property relationship, equivalence anddisjointness, and relationships between properties.• Individual axioms: statements about individuals (sameIndividual,differentIndividuals).
  41. 41. Semantics on theWeb41Semantic Web StackBerners-Lee (2006)SPARQL – * Protocol and RDF Query Language
  42. 42. Semantics on theWeb42SPARQL – * Protocol and RDF Query Language• Query language designed to use a syntax similar toSQL for retrieving data from relational databases.• Different query forms:• SELECT returns variables and their bindings directly.• CONSTRUCT returns a single RDF graph specified by agraph template.• ASK test whether or not a query pattern has a solution.Returns yes/no.• DESCRIBE returns a single RDF graph containing RDFdata about resources.
  43. 43. Semantics on theWeb43SPARQL – * Protocol and RDF Query Language• The syntax of a SELECT query is as follows:– SELECT nominates which components of the matchesmade against the data should be returned.– FROM (optional) indicates the sources for the data againstwhich to find matches.– WHERE defines patterns to match against the data.– ORDER BY defines a means to order the selectedmatches.
  44. 44. Semantics on theWeb44SPARQL – * Protocol and RDF Query LanguagePREFIX dc: <>PREFIX foaf: <>PREFIX music-ont: <>SELECT ?album_name ?track_titleWHERE {<>foaf:made ?album .?album dc:title ?album_name ;music-ont:track ?track .?track dc:title ?track_title . }Retrieve the names of the albums and tracks recorded byThe Beatles.
  45. 45. Semantics on theWeb45SPARQL – * Protocol and RDF Query LanguageSQL SPARQLBased on relations (tables). Based on labelled directed graphs.The relations (tables) to bematched over should beindicated.Assumes a default graph.(The FROM clause populates thiswith specific identifiedsubgraphs).(Retrieval) queries produce arelation from a relation.SPARQL SELECT queries produce arelation from a graph.CONSTRUCT queries (consideredlater) produce a graph from agraph.
  46. 46. Semantics on theWeb46SPARQL – * Protocol and RDF Query Language• SPARQL 1.1 provides graph update operations:• INSERT DATA: adds explicit triples, given inline.• DELETE DATA: removes explicit triples, given inline.• DELETE/INSERT WHERE: updates based on triples calculatedfrom WHERE clause (as in SELECT and CONSTRUCT).• LOAD: reads the content of a document into a graph.• COPY/MOVE/APPEND: manipulates at named graph level.• CLEAR/DROP: removes all triples in one or more graph.
  47. 47. Semantics on theWeb47SPARQL – * Protocol and RDF Query LanguagePREFIX dc: <>PREFIX foaf: <>INSERT DATA { GRAPH <http://myFavGroups/The_Beatles> {<>foaf:made <> ,<> .<>dc:title "Please Please Me".< >dc:title "Something New". } }Insert the following albums recorded byThe Beatles into the graphhttp://myFavGroups/The_Beatles
  48. 48. Semantics on theWeb48SPARQL – * Protocol and RDF Query LanguagePREFIX dc: <>PREFIX foaf: <>DELETE { ?album ?predicate ?object . }WHERE {<>foaf:made ?album .?album dc:title "Casualities";?predicate ?object .}Delete all the information about the album Casualities of The Beatles.
  50. 50. Linked Data50• Set of best practices for publishing dataon the Web.• Data from different knowledgedomains, self-described,linked and accessible.• Follows 4 simple principles…
  51. 51. Linked Data Principles1. Use URIs as names for things.2. Use HTTP URIs so that users can look upthose names.3. When someone looks up a URI, provideuseful information, using the standards(RDF*, SPARQL).4. Include links to other URIs, so that userscan discover more things.51
  52. 52. Linked Data Principles• A foundational issue in Linked Data was thedistinction of URIs for object documents that mightdescribe them.521. Use URIs as names for things.
  53. 53. Linked Data Principles• HTTP allows a second way to distinguish real-worldobjects from documents.• Best practice says HTTP 303 and Location headershould be used.532. Use HTTP URIs so user can look up those names.
  54. 54. • While RDF/XML should be the default for look-up.• RDFa annotations in HTML are now also standard.• SPARQL endpoint for queries are encouraged, or adump of the whole dataset.Linked Data Principles543. When someone looks up a URI, provide usefulinformation, using the standards (RDF*, SPARQL,Turtle1).1 To become a standard.
  55. 55. What to return for a URI?• Immediate description: triples where the URI is the subject.• Backlinks: triples where the URI is the object.• Related descriptions: information of interest in typical usage scenarios.• Metadata: information as author and licensing information.• Syntax: RDF descriptions as RDF/XML and human-readable formats.Linked Data Principles553. When someone looks up a URI, provide usefulinformation, using the standards (RDF*, SPARQL,Turtle1).Source: How to Publish Linked Data on The Web - Chris Bizer, Richard Cyganiak, Tom Heath.
  56. 56. There are several ways to reuse URIs:• direct reuse• (OWL) sameAs• (RDFS) seeAlso• direct reuse of class/property• (RDFS) sub-class/-property• (OWL) equivalent class/property• SKOS broad matchLinked Data Principles564. Include links to other URIs, so that users candiscover more things.Instance LevelSchema Level
  57. 57. Linked Data 5 Star57Data is available on the Web.Data is available as machine-readable structured data.Non-propietary formats are used.Individual data identified with open standards.Data is linked to other data provider.
  58. 58. Linked Data 5 Star58Example:"John Lennon""Paul McCartney""George Harrison""Ringo Starr"My Data
  59. 59. Linked Data 5 Star59Data is available on the Web"John Lennon""Paul McCartney""George Harrison""Ringo Starr"My DataIt can be retrieved using HTTP.
  60. 60. Linked Data 5 Star60Data is available as machine-readable structured data"John Lennon""Paul McCartney""George Harrison""Ringo Starr"My Data"The Beatles" Please Me – 1963A Hard Day‘s Night – 1964Help! – 1965Revolver – 1966…ImagesScanned InformationPlain text or …(to continue on the next slide)Machine-readable data:
  61. 61. Non-propietary formats are used<schema ""version= "1.0" ><band><name>The Beatles</name><member>John Lennon</member><member>Paul McCartney</member><member>George Harrison</member><member>Ringo Starr</member><picture></picture><album year=1963>Please Please Me</album><album year=1964>A Hard Day‘s Night</album><album year=1965>Help!</album><album year=1966>Revolver</album>…</band>Linked Data 5 Star61My Data
  62. 62. Linked Data 5 Star62Individual data identified with open standards<schema""version= "1.0" ><band><name></name><member></member>...<albumyear=1963></album>…</band>My DataIn this context, "Revolver" is analbum! Not a gun.URI: Uniform Resource Identifier• Data is uniquely identifiedThe BeatlesJohn LennonRevolver• Dissambiguation
  63. 63. Linked Data 5 Star63Data is linked to other data provider<schema""version= "1.0" ><band><name></name><member></member>...<albumyear=1963></album>…<seeAlso></seeAlso></band>
  64. 64. Linked Data Cloud642007
  65. 65. Linked Data Cloud652008
  66. 66. Linked Data Cloud662009
  67. 67. Linked Data Cloud672010
  68. 68. Linked Data Cloud682011
  69. 69. Linked Data Cloud692012
  70. 70. State of the LOD Cloud170• Total Datasets:2951 Version 0.3, 09/19/2011• Total Triples:31,634,213,770Distribution of triples by domain
  71. 71. State of the LOD Cloud171• Total (Out-)Links:503,998,8291 Version 0.3, 09/19/2011 of links by domain
  72. 72. Exploring theWeb of Data72• Linked Data browsers• Linked Data mashups• Search engines
  73. 73. Linked Data Browsers73http://marbles.sourceforge.netMarbles
  74. 74. Linked Data Mashup74
  75. 75. Linked Data Mashup75DBPedia MobilePictures from revyu.com
  76. 76. Linked Data Mashup76http://sig.maSIGMA
  77. 77. Linked Data Search Engines77
  78. 78. Some Application Scenarios78BBC
  79. 79. Some Application
  80. 80. Some Application Scenarios80Linked Government Data: USA
  81. 81. Some Application Scenarios81Linked Government Data: UK
  82. 82. Summary82In this chapter we studied:• The Web and its evolution.• Web technology basics: HTTP, HTML, URI.• Vocabularies to describe data.• The Semantic Web stack: RDF, RDF-S, OWL, SPARQL.• Linked Data concept and principles.• Evolution of the LOD cloud.• Browsers, mashups and search engines to explore the Webof Data.• Some application scenarios.
  83. 83. For exercises, quiz and further material visit our website:EUCLID - Providing Linked Data 83@euclid_project euclidproject euclidprojecthttp://www.euclid-project.euOther channels:eBook Course
  84. 84. Acknowledgements• Alexander Mikroyannidis• Alice Carpentier• Andreas Harth• Andreas Wagner• Andriy Nikolov• Barry Norton• Daniel M. Herzig• Elena Simperl• Günter Ladwig• Inga Shamkhalov• Jacek Kopecky• John Domingue
• Juan Sequeda• Kalina Bontcheva• Maria Maleshkova• Maria-Esther Vidal• Maribel Acosta• Michael Meier• Ning Li• Paul Mulholland• Peter Haase• Richard Power• Steffen Stadtmüller84
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This presentation introduces the main principles of Linked Data, the underlying technologies and background standards. It provides basic knowledge for how data can be published over the Web, how it can be queried, and what are the possible use cases and benefits. As an example, we use the development of a music portal (based on the MusicBrainz dataset), which facilitates access to a wide range of information and multimedia resources relating to music.


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