Linked Data: Evolving the Web into a Global Data Space

137 Pages·2011·2.174 MB·English

by  Tom Heath, Christian Bizer

Series ISSN: 2153-5418 H
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SYNTHESIS LECTURES ON TH &C Morgan & Claypool Publishers
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THE SEMANTIC WEB: THEORY AND TECHNOLOGY B
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Series Editors: James Hendler, Rensselaer Polytechnic Institute
Linked Data
Linked Data
Evolving the Web into a
Evolving the Web into a Global Data Space
Tom Heath, Talis • Christian Bizer, Freie Universität Berlin
Global Data Space
The World Wide Web has enabled the creation of a global information space comprising linked
documents. As the Web becomes ever more enmeshed with our daily lives, there is a growing desire
for direct access to raw data not currently available on the Web or bound up in hypertext documents.
Linked Data provides a publishing paradigm in which not only documents, but also data, can be a first
L
class citizen of the Web, thereby enabling the extension of the Web with a global data space based on IN
open standards — the Web of Data. In this Synthesis lecture we provide readers with a detailed K
E
technical introduction to Linked Data. We begin by outlining the basic principles of Linked Data, D

including coverage of relevant aspects of Web architecture. The remainder of the text is based around D
A
two main themes — the publication and consumption of Linked Data. Drawing on a practical Linked T
A Tom Heath
Data scenario, we provide guidance and best practices on: architectural approaches to publishing Linked
Data; choosing URLs and vocabularies to identify and describe resources; deciding what data to return
in a description of a resource on the Web; methods and frameworks for automated linking of data Christian Bizer
sets; and testing and debugging approaches for Linked Data deployments. We give an overview of
existing Linked Data applications and then examine the architectures that are used to consume Linked
Data from the Web, alongside existing tools and frameworks that enable these. Readers can expect
to gain a rich technical understanding of Linked Data fundamentals, as the basis for application
development, research or further study.
About SYNTHESIs
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Digital Library of Engineering and Computer Science. Synthesis Lectures
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provide concise, original presentations of important research and development A
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SYNTHESIS LECTURES ON
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ISBN: 978-1-60845-430-3 A
Morgan & Claypool Publishers 90000 Y THE SEMANTIC WEB: THEORY AND TECHNOLOGY
P
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www.morganclaypool.com James Hendler, Series Editor
9 781608 454303 O
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Linked Data
EvolvingtheWebintoaGlobalDataSpace

Synthesis Lectures on the
Semantic Web: Theory and
Technology
Editors
JamesHendler,RensselaerPolytechnicInstitute
FrankvanHarmelen,VrijeUniversiteitAmsterdam
WhetheryoucallittheSemanticWeb,LinkedData,orWeb3.0,anewgenerationofWeb
technologiesisofferingmajoradvancesintheevolutionoftheWorldWideWeb.Asthefirst
generationofthistechnologytransitionsoutofthelaboratory,newresearchisexploringhowthe
growingWebofDatawillchangeourworld.Whiletopicssuchasontology-buildingandlogicsremain
vital,newareassuchastheuseofsemanticsinWebsearch,thelinkinganduseofopendataonthe
Web,andfutureapplicationsthatwillbesupportedbythesetechnologiesarebecomingimportant
researchareasintheirownright.Whethertheybescientists,engineersorpractitioners,Webusers
increasinglyneedtounderstandnotjustthenewtechnologiesoftheSemanticWeb,buttounderstand
theprinciplesbywhichthosetechnologieswork,andthebestpracticesforassemblingsystemsthat
integratethedifferentlanguages,resources,andfunctionalitiesthatwillbeimportantinkeepingthe
Webtherapidlyexpanding,andconstantlychanging,informationspacethathaschangedourlives.
Topicstobecovered:
• SemanticWebPrinciplesfromlinked-datatoontologydesign
• KeySemanticWebtechnologiesandalgorithms
• SemanticSearchandlanguagetechnologies
• TheEmerging“WebofData”anditsuseinindustry,governmentanduniversityapplications
• Trust,SocialnetworkingandcollaborationtechnologiesfortheSemanticWeb
• TheeconomicsofSemanticWebapplicationadoptionanduse
• PublishingandScienceontheSemanticWeb
• SemanticWebinhealthcareandlifesciences
LinkedData:EvolvingtheWebintoaGlobalDataSpace
TomHeathandChristianBizer
2011
Copyright© 2011byMorgan&Claypool
Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedin
anyformorbyanymeans—electronic,mechanical,photocopy,recording,oranyotherexceptforbriefquotationsin
printedreviews,withoutthepriorpermissionofthepublisher.
LinkedData:EvolvingtheWebintoaGlobalDataSpace
TomHeathandChristianBizer
www.morganclaypool.com
ISBN:9781608454303 paperback
ISBN:9781608454310 ebook
DOI10.2200/S00334ED1V01Y201102WBE001
APublicationintheMorgan&ClaypoolPublishersseries
SYNTHESISLECTURESONTHESEMANTICWEB:THEORYANDTECHNOLOGY
Lecture#1
SeriesEditors:JamesHendler,RensselaerPolytechnicInstitute
FrankvanHarmelen,VrijeUniversiteitAmsterdam
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Linked Data
EvolvingtheWebintoaGlobalDataSpace
Tom Heath
Talis
Christian Bizer
FreieUniversitätBerlin
SYNTHESISLECTURESONTHESEMANTICWEB:THEORYAND
TECHNOLOGY#1
M
&C Morgan &cLaypool publishers
ABSTRACT
The World Wide Web has enabled the creation of a global information space comprising linked
documents.AstheWebbecomesevermoreenmeshedwithourdailylives,thereisagrowingdesire
fordirectaccesstorawdatanotcurrentlyavailableontheWeborboundupinhypertextdocuments.
LinkedDataprovidesapublishingparadigminwhichnotonlydocuments,butalsodata,canbea
first class citizen of the Web,thereby enabling the extension of the Web with a global data space
based on open standards - the Web of Data. In this Synthesis lecture we provide readers with
a detailed technical introduction to Linked Data. We begin by outlining the basic principles of
LinkedData,includingcoverageofrelevantaspectsofWebarchitecture.Theremainderofthetext
isbasedaroundtwomainthemes-thepublicationandconsumptionofLinkedData.Drawingona
practicalLinkedDatascenario,weprovideguidanceandbestpracticeson:architecturalapproaches
to publishing Linked Data; choosing URIs and vocabularies to identify and describe resources;
decidingwhatdatatoreturninadescriptionofaresourceontheWeb;methodsandframeworksfor
automatedlinkingofdatasets;andtestinganddebuggingapproachesforLinkedDatadeployments.
WegiveanoverviewofexistingLinkedDataapplicationsandthenexaminethearchitecturesthat
areusedtoconsumeLinkedDatafromtheWeb,alongsideexistingtoolsandframeworksthatenable
these.Readers can expect to gain a rich technical understanding of Linked Data fundamentals,as
thebasisforapplicationdevelopment,researchorfurtherstudy.
KEYWORDS
web technology, databases, linked data, web of data, semantic web, world wide web,
dataspaces,dataintegration,datamanagement,webengineering,resourcedescription
framework
vii
Contents
ListofFigures ........................................................... xi
Preface .................................................................xiii
1 Introduction ..............................................................1
1.1 TheDataDeluge ....................................................... 1
1.2 TheRationaleforLinkedData ........................................... 2
1.2.1 StructureEnablesSophisticatedProcessing........................... 2
1.2.2 HyperlinksConnectDistributedData ............................... 3
1.3 FromDataIslandstoaGlobalDataSpace ................................. 4
1.4 IntroducingBigLynxProductions ........................................ 5
2 PrinciplesofLinkedData ..................................................7
2.1 ThePrinciplesinaNutshell .............................................. 7
2.2 NamingThingswithURIs............................................... 9
2.3 MakingURIsDefererenceable........................................... 10
2.3.1 303URIs....................................................... 11
2.3.2 HashURIs ..................................................... 13
2.3.3 Hashversus303................................................. 14
2.4 ProvidingUsefulRDFInformation ...................................... 15
2.4.1 TheRDFDataModel ........................................... 15
2.4.2 RDFSerializationFormats ....................................... 18
2.5 IncludingLinkstootherThings ......................................... 20
2.5.1 RelationshipLinks............................................... 21
2.5.2 IdentityLinks................................................... 22
2.5.3 VocabularyLinks ................................................ 24
2.6 Conclusions .......................................................... 25
3 TheWebofData ........................................................ 29
3.1 BootstrappingtheWebofData.......................................... 30
3.2 TopologyoftheWebofData............................................ 30
3.2.1 Cross-DomainData ............................................. 33
viii
3.2.2 GeographicData ................................................ 34
3.2.3 MediaData..................................................... 34
3.2.4 GovernmentData ............................................... 35
3.2.5 LibrariesandEducation .......................................... 36
3.2.6 LifeSciencesData............................................... 37
3.2.7 RetailandCommerce ............................................ 38
3.2.8 UserGeneratedContentandSocialMedia.......................... 38
3.3 Conclusions .......................................................... 39
4 LinkedDataDesignConsiderations....................................... 41
4.1 UsingURIsasNamesforThings ........................................ 41
4.1.1 MintingHTTPURIs............................................ 41
4.1.2 GuidelinesforCreatingCoolURIs ................................ 42
4.1.3 ExampleURIs .................................................. 43
4.2 DescribingThingswithRDF ........................................... 44
4.2.1 LiteralTriplesandOutgoingLinks ................................ 45
4.2.2 IncomingLinks ................................................. 46
4.2.3 TriplesthatDescribeRelatedResources............................. 46
4.2.4 TriplesthatDescribetheDescription............................... 47
4.3 PublishingDataaboutData............................................. 48
4.3.1 DescribingaDataSet ............................................ 48
4.3.2 ProvenanceMetadata ............................................ 52
4.3.3 Licenses,WaiversandNormsforData.............................. 52
4.4 ChoosingandUsingVocabulariestoDescribeData......................... 56
4.4.1 SKOS,RDFSandOWL ......................................... 56
4.4.2 RDFSBasics ................................................... 57
4.4.3 ALittleOWL .................................................. 60
4.4.4 ReusingExistingTerms .......................................... 61
4.4.5 SelectingVocabularies............................................ 62
4.4.6 DefiningTerms ................................................. 63
4.5 MakingLinkswithRDF ............................................... 64
4.5.1 MakingLinkswithinaDataSet................................... 64
4.5.2 MakingLinkswithExternalDataSources .......................... 64
4.5.3 SettingRDFLinksManually ..................................... 66
4.5.4 Auto-generatingRDFLinks ...................................... 66
ix
5 RecipesforPublishingLinkedData ....................................... 69
5.1 LinkedDataPublishingPatterns......................................... 69
5.1.1 PatternsinaNutshell ............................................ 69
5.1.2 AdditionalConsiderations ........................................ 71
5.2 TheRecipes .......................................................... 72
5.2.1 ServingLinkedDataasStaticRDF/XMLFiles ..................... 72
5.2.2 ServingLinkedDataasRDFEmbeddedinHTMLFiles ............. 74
5.2.3 ServingRDFandHTMLwithCustomServer-SideScripts........... 77
5.2.4 ServingLinkedDatafromRelationalDatabases ..................... 77
5.2.5 ServingLinkedDatafromRDFTripleStores ....................... 79
5.2.6 ServingLinkedDatabyWrappingExistingApplicationorWebAPIs .. 79
5.3 AdditionalApproachestoPublishingLinkedData ......................... 80
5.4 TestingandDebuggingLinkedData ..................................... 80
5.5 LinkedDataPublishingChecklist ....................................... 82
6 ConsumingLinkedData ................................................. 85
6.1 DeployedLinkedDataApplications...................................... 85
6.1.1 GenericApplications............................................. 86
6.1.2 Domain-specificApplications ..................................... 90
6.2 DevelopingaLinkedDataMashup ...................................... 93
6.2.1 SoftwareRequirements........................................... 94
6.2.2 AccessingLinkedDataURIs...................................... 94
6.2.3 RepresentingDataLocallyusingNamedGraphs..................... 95
6.2.4 QueryingLocalDatawithSPARQL............................... 96
6.3 ArchitectureofLinkedDataApplications ................................. 97
6.3.1 AccessingtheWebofData ...................................... 100
6.3.2 VocabularyMapping ............................................ 101
6.3.3 IdentityResolution ............................................. 102
6.3.4 ProvenanceTracking ............................................ 103
6.3.5 DataQualityAssessment ........................................ 103
6.3.6 CachingWebDataLocally ...................................... 105
6.3.7 UsingWebDataintheApplicationContext........................ 105
6.4 EffortDistributionbetweenPublishers,ConsumersandThirdParties........ 105