The document discusses representing data in the Resource Description Framework (RDF). It describes how relational data can be represented as RDF triples with rows becoming subjects, columns becoming properties, and values becoming objects. It also discusses using URIs instead of internal IDs and names to allow data integration. The document then covers serializing RDF data in different formats like RDF/XML, N-Triples, N3, and Turtle and describes syntax for representing literals, language tags, and abbreviating subject and predicate pairs.

1. Emanuele Della Valle [email_address] http://emanueledellavalle.org Data in RDF

2. Share, Remix, Reuse — Legally This work is licensed under the Creative Commons Attribution 3.0 Unported License. Your are free: to Share — to copy, distribute and transmit the work to Remix — to adapt the work Under the following conditions Attribution — You must attribute the work by inserting “ © applied-semantic-web.org” at the end of each reused slide a credits slide stating: these slides are partially based on “Data in RDF” by Emanuele Della Valle http://applied-semantic-web.org/2010/03/02_RDF.ppt To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/

3. Data Interchange: RDF

4. RDF in a nutshell Looking for a flexible data model Why Application are always changing (competitive environment) People are always adding more features Graceful evolution is important Optimal: relational model Relational model is remarkably flexible Supports graceful evolution Change => Add another table Existing queries are unaffected Easily accommodates new data Without affecting existing queries Allows data to be easily combined ("joined") in new ways 25+ years of relational database experience

5. RDF in a nutshell Resource Description Framework The adaptation of the relational model to the Web give rise to RDF From tuples to triples Any relational data can be represented as triples Row Key --> Subject Column --> Property Value --> Value

6. RDF in a nutshell Representing relational data in RDF (almost) E.g., drug data Represented in RDF (almost) BB.2 Anxiolytics C 16 H 21 NO 2 Propranolol Propranololo プロプラノロール Category Formula Is a Drug Legend resource literal Name Drug Category Formula BB.2 Anxiolytics C 16 H 21 NO 2 Drug Name BB.2 Propranolol BB.2 Propranololo BB.2 プロプラノロール

7. RDF in a nutshell Representing relational data in RDF (almost) Two important problems Once out of the database internal ID (e.g., BB.2) becomes useless Once out of the database internal names of schema element (e.g., Category) becomes useless as well RDF solves it by using URI Internal ID should be replaced by URI Internal schema names should be replaced by URI Values do (always) not need to be URI-fied http://dbpedia.org/resource/Propranolol http://dbpedia.org/resource/Category:Anxiolytics C16H21NO2 http://www.w3.org/2004/02/skos/core#subject http://dbpedia.org/ontology/formula http://www.w3.org/2000/01/rdf-schema#label http://dbpedia.org/ontology/Drug http://www.w3.org/1999/02/22-rdf-syntax-ns#type Legend resource literal Propranolol Propranololo プロプラノロール

8. Which URI should we use? Popular ones! Data merge will take place automatically! RDF in a nutshell Representing data in RDF Q/A 1/4 http://dbpedia.org/resource/Propranolol http://dbpedia.org/resource/Category:Anxiolytics http://www.w3.org/2004/02/skos/core#subject + http://dbpedia.org/resource/Propranolol http://dbpedia.org/ontology/knownFor http://dbpedia.org/resource/Propranolol http://dbpedia.org/resource/Category:Anxiolytics http://www.w3.org/2004/02/skos/core#subject = http://dbpedia.org/ontology/knownFor http://dbpedia.org/resource/James_W._Black http://dbpedia.org/resource/James_W._Black

9. Where do I find popular URIs? A difficult question with no clear answer The best place to keep an eye on is the Linking Open Data Project http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData and in particular the following pages of the Wiki Data Sets http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/DataSets Semantic Web Search Engines http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/SemanticWebSearchEngines Common Vocabularies http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/CommonVocabularies I normally use Sindice API through sameas.org e.g. http://sameas.org/html?q=propranolol&x=0&y=0 RDF in a nutshell Representing data in RDF Q/A 2/4

10. What is a value? When shall we URI-fy a value? Literals cannot be used to merge different data set E.g., what if we what to merge two resources based on their labels? BRCA may refer to different thing on the Web e.g., try http://en.wikipedia.org/wiki/BRCA URI-fy any value that can be eventually used to merge different dataset and leave the other values as literals RDF in a nutshell Representing data in RDF Q/A 3/4 BRCA http://www.w3.org/2000/01/rdf-schema#label BRCA http://www.w3.org/2000/01/rdf-schema#label + = ?

11. RDF in a nutshell Other data structure in RDF Trees can be represented in RDF Anything can be represented in RDF

12. RDF in a nutshell Serializing RDF Three alternatives to write triples, in RDF/XML: Standard serialization in XML <Description about=”subject”> <property>value</property> </Description> e.g., http://dbpedia.org/data/Propranolol.rdf Check-out the triples using http://www.w3.org/RDF/Validator/ NTriples: Simple (verbose) reference serialization (for specifications only) ‏ <http:// ... subject> <http:// ... predicate> “value” . http://www.w3.org/RDF/Validator/ARPServlet?URI=http%3A%2F%2Fdbpedia.org%2Fresource%2FPropranolol&PARSE=Parse+URI%3A+&TRIPLES_AND_GRAPH=PRINT_TRIPLES&FORMAT=PNG_EMBED N3 and Turtle: Developer-friendly serializations :subject :property “value” . e.g. http://dbpedia.org/data/Propranolol.n3

13. RDF in a nutshell Serializing RDF in Turtle - namespaces URI terms can be abbreviated using namespaces @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix dbpedia: <http://dbpedia.org/resource/> . @prefix dbpedia-owl: <http://dbpedia.org/ontology/> . dbpedia:Propranolol rdf:type dbpedia-owl:Drug . <http://www.w3.org/1999/ 02/22-rdf-syntax-ns#type> = ' a ' dbpedia:Propranolol a dbpedia-owl:Drug .

14. RDF in a nutshell Serializing RDF in Turtle - Literals Literals: &quot;Propranolol&quot; Literals with language tags: &quot; プロプラノロール &quot;@jp @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . dbpedia:Propranolol rdfs:label &quot;Propranolol&quot;@en . dbpedia:Propranolol rdfs:label &quot;Propranololo&quot;@it . dbpedia:Propranolol rdfs:label &quot; プロプラノロール &quot;@jp . Typed literals: &quot;3.14&quot;^^xsd:float dbpedia:Propranolol dbpprop:molecularWeight &quot;259.34&quot;^^xsd:float .

15. RDF in a nutshell Serializing RDF in Turtle - Convience Syntax Abbreviating repeated subjects: dbpedia:Propranolol rdfs:label &quot;Propranololo&quot;@it . dbpedia:Propranolol dbpprop:molecularWeight &quot;259.34&quot;^^xsd:float . ... is the same as ... dbpedia:Propranolol rdfs:label &quot;Propranololo&quot;@it ; dbpprop:molecularWeight &quot;259.34&quot;^^xsd:float . Abbreviating repeated subject/predicate pairs: dbpedia:Propranolol rdfs:label &quot;Propranolol&quot;@en . dbpedia:Propranolol rdfs:label &quot;Propranololo&quot;@it . dbpedia:Propranolol rdfs:label &quot; プロプラノロール &quot;@cn . ... is the same as ... dbpedia:Propranolol rdfs:label &quot;Propranolol&quot;@en , &quot;Propranololo&quot;@it , &quot; プロプラノロール &quot;@cn .

16. RDF in a nutshell Serializing RDF in XML - basics W3C standardized an RDF/XML syntax [1] The basic idea is to insert an XML element for each node (sobject and value) and arch (predicate) Es. < rdf:RDF xmlns:rdf=&quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#” xmlns:skos=&quot;http://www.w3.org/2004/02/skos/core#&quot; < rdf:Description rdf:about =&quot;http://dbpedia.org/resource/Propranolol&quot;> < skos:subject > < rdf:Description rdf:about =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </ skos:subject > </rdf:Description> </rdf:RDF> [1] RDF/XML Syntax Specification available at http://www.w3.org/TR/rdf-syntax-grammar/ dbpedia:Propranolol category:Anxiolytics skos:subject property element Root tag

17. RDF in a nutshell Serializing RDF in XML - abbreviation A possible abbreviation is using rdf:resource in the property elements Es. < rdf:RDF xmlns:rdf=&quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#” xmlns:skos=&quot;http://www.w3.org/2004/02/skos/core#&quot; <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Propranolol&quot;> <skos:subject rdf:resource =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </rdf:Description> </rdf:RDF>

18. RDF in a nutshell Serializing RDF in XML - abbreviation Encoding Literals datatype <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Propranolol&quot;> <dbpprop:molecularWeight rdf:datatype=&quot;http://www.w3.org/2001/XMLSchema#float&quot; >259.34 </dbpprop:molecularWeight > </rdf:Description> Language tag <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Propranolol&quot;> <rdfs:label xml:lang=&quot;it&quot;> Propranololo </rdfs:label > </rdf:Description> dbpedia:Propranolol dbpprop:molecularWeight dbpedia:Propranolol rdfs:label “ Propranololo”@it &quot;259.34&quot;^^xsd:float

19. RDF in a nutshell Serializing RDF in XML – rdf:type abbreviation It’s possible to abbreviate rdf:type Es. Long form <rdf:Description rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot;> <rdf:type rdf:resource=&quot;http://dbpedia.org/ontology/Drug&quot;/> </rdf:Description> Abbreviated form <dbpedia-owl:Drug rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot; /> dbpedia:Propranolol http://dbpedia.org/ontology/Drug rdf:type

20. RDF in a nutshell Serializing RDF in XML – more statements 1/3 E.g. can be listed <rdf:Description rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot;> <rdf:type rdf:resource=&quot;http://dbpedia.org/ontology/Drug&quot;/> </rdf:Description> <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Propranolol&quot;> <skos:subject rdf:resource =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </rdf:Description> nested <rdf:Description rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot;> <rdf:type rdf:resource=&quot;http://dbpedia.org/ontology/Drug&quot;/> <skos:subject rdf:resource =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </rdf:Description> shortened to a minimum <dbpedia-owl:Drug rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot; > <skos:subject rdf:resource =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </dbpedia-owl:Drug> dbpedia:Propranolol category:Anxiolytics skos:subject http://dbpedia.org/ontology/Drug

21. RDF in a nutshell Serializing RDF in XML – more statements 2/3 E.g. can be listed <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Propranolol&quot;> <skos:subject rdf:resource =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;/> </rdf:Description> <rdf:Description rdf:about=&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;> <skos:broader rdf:resource =&quot;http://dbpedia.org/resource/Category:Psycholeptics&quot;/> </rdf:Description> nested <rdf:Description rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot;> <skos:subject> <rdf:Description rdf:about =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;> <skos:broader rdf:resource =&quot;http://dbpedia.org/resource/Category:Psycholeptics&quot;/> </rdf:Description> </skos:subject> </rdf:Description> dbpedia:Propranolol category:Anxiolytics skos:subject Category:Psycholeptics skos:broader

22. RDF in a nutshell Serializing RDF in XML – more statements 3/3 E.g. Applying all abbreviations becomes <dbpedia-owl:Drug rdf:about=&quot; http://dbpedia.org/resource/Propranolol &quot; > <rdfs:label xml:lang=&quot;it&quot;>Propranololo</rdfs:label> <skos:subject> <skos:concept r df:about =&quot;http://dbpedia.org/resource/Category:Anxiolytics&quot;> <skos:broader> <skos:concept r df:about =&quot;http://dbpedia.org/resource/Category:Psycholeptics&quot;/> </skos:broader> </skos:concept> </skos:subject> </dbpedia-owl:Drug> dbpedia:Propranolol category:Anxiolytics skos:subject Category:Psycholeptics skos:broader http://dbpedia.org/ontology/Drug skos:concept “ Propranololo”@it rdfs:label

23. RDF in a nutshell Merging XML files (representing an RDF model) Suppose you have to merge the two following XML Merging the XML trees is difficult, but being RDF … <Drug rdf:about=&quot;Propranolol&quot;> <skos:subject> <skos:concept rdf:about=&quot;Anxiolytics&quot;/> </skos:subject > <excretion> <AnatomicalStructure rdf:about=&quot;Kidney&quot;/> </excretion> </Drug> <skos:concept rdf:about=&quot; Anxiolytics &quot; skos:isSubjectOf=&quot; Propranolol &quot;> <canDamage> < AnatomicalStructure rdf:about=&quot; Kidney &quot;/> </canDamage> </skos:concept> Propranolol Anxiolytics Drug rdf : type rdf : type skos:subject Concept Kidney rdf : type AnatomicalStructure excretion Propranolol Anxiolytics rdf : type Concept Kidney rdf : type AnatomicalStructure canDamage skos:isSubjectOf

24. RDF in a nutshell Merging XML files 2/2 It’s (just) a matter to merge the two RDF graphs NOTE: It works out nicely because both RDF/XML documents refer to the same resources and use the same vocabularies. U Propranolol Anxiolytics Drug rdf : type rdf : type skos:subject Concept Kidney AnatomicalStructure canDamage excretion skos:isSubjectOf rdf : type

25. Publishing RDF as Linked Data Principles Things must be identified with dereferenceable HTTP URIs. If such a URI is dereferenced asking for the MIME-type application/rdf+xml, a data source must return an RDF/XML description of the identified resource. Information Resources Non-Information Resources Besides RDF links to resources within the same data source, RDF descriptions should also contain RDF links to resources provided by other data sources

26. Publishing RDF as Linked Data More on Content Negotiation Approach E.g. Resource identifier http://dbpedia.org/resource/Propranolol RDF representation describing Propranolol http://dbpedia.org/ data /Propranolol .rdf HTML representation describing Propranolol http://dbpedia.org/ page /Propranolol Test it! http://idi.fundacionctic.org/vapour

27. Publishing RDF as Linked Data Recipes for Serving Information as Linked Data Recipes [1] Serving static RDF files Serving information stored in a DB as (virtual) RDF Using a RDF storage with a Linked Data Interface Wrap API to serve (virtual) RDF [1] http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/

28. Publishing RDF as Linked Data Recipe 1 - Serving static RDF files 1/3 IDEA: negotiate content using Apache mod_rewrite by writing a .htaccess file Directory layout apachedocumentroot/ examples/ .htaccess content/ file.html file.rdf Expected behavior Requesting http://localhost/examples/file a HTML browser is redirected to http://localhost/examples/content/file.html a Linked Data application is redirected to http://localhost/examples/content/file.rdf

29. Publishing RDF as Linked Data Recipe 1 - Serving static RDF files 2/3 # Turn off MultiViews Options –MultiViews # Rewrite engine setup RewriteEngine On RewriteBase /examples # Rewrite rule to serve HTML content from the vocabulary URI if requested RewriteCond %{HTTP_ACCEPT} !application/rdf\+xml.*(text/html|application/xhtml\+xml) RewriteCond %{HTTP_ACCEPT} text/html [OR] RewriteCond %{HTTP_ACCEPT} application/xhtml\+xml [OR] RewriteCond %{HTTP_USER_AGENT} ^Mozilla/.* RewriteRule ^example/$ content/file.html [R=303] # Rewrite rule to serve RDF/XML content if requested RewriteCond %{HTTP_ACCEPT} application/rdf\+xml RewriteRule ^example/ content/file.rdf [R=303] # Rewrite rule to serve RDF/XML content by default RewriteRule ^example/ content/file.rdf [R=303] [source: http://www.w3.org/TR/swbp-vocab-pub/#recipe4example ]

30. Publishing RDF as Linked Data Recipe 1 - Serving static RDF files 3/3 Testing the configuration http://localhost/examples/ file http://localhost/examples/ content/file.html http://localhost/examples/content/file.html http://localhost/examples/ file http://localhost/examples/ content/file.rdf http://localhost/examples/content/file.rdf

31. Publishing RDF as Linked Data Recipe 2 - DB as (virtual) RDF General Idea Ready to use solutions D2R Server http://sites.wiwiss.fu-berlin.de/suhl/bizer/d2r-server/index.html#quickstart OpenLink Virtuoso http://virtuoso.openlinksw.com/Whitepapers/pdf/Virtuoso_SQL_to_RDF_Mapping.pdf http://virtuoso.openlinksw.com/Whitepapers/pdf/Deploying_Linked_Data_Final1.pdf Triplify http://triplify.org/Overview

32. Publishing RDF as Linked Data Recipe 3 - RDF storage + Linked Data Interface General Idea Ready to use solutions Pubby : a Linked Data interfaces to SPARQL endpoints. http://www4.wiwiss.fu-berlin.de/pubby/

33. Publishing RDF as Linked Data Recipe 4 - Wrap API to serve (virtual) RDF General Idea No “general” solutions, only ad hoc ones Virtuoso Sponger : a framework for developing Linked Data wrappers (called cartridges) around different types of data sources http://virtuoso.openlinksw.com/dataspace/dav/wiki/Main/VirtSponger http://virtuoso.openlinksw.com/dataspace/dav/wiki/Main/VirtSpongerCartridgeSupportedDataSources SIOC Exporters http://sioc-project.org/exporters [source http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/Bizer-ESWC2007-RDFbookmashup.pdf ]

34. Publishing RDF as Linked Data Which recipe should I use? How much data do you want to serve? several hundred RDF triples: recipe 1 Larger dataset: recipe 2, 3 and 4 How is your data currently stored? In a relational database: recipe 2 Available through an API: recipe 4 As RDF dump: recipe 3 How often does your data change? Frequently: recipe 2 and 4 Rarely: recipe 1 and 3

35. RDF in a nutshell RDF Resources RDF at the W3C - primer and specifications http://www.w3.org/RDF/ Semantic Web tools - community maintained list; includes triple store, programming environments, tool sets, and more http://esw.w3.org/topic/SemanticWebTools 302 Semantic Web Videos and Podcasts - includes a section specifically on RDF videos http://www.semanticfocus.com/blog/entry/title/302-semantic-web-videos-and-podcasts/

36. credits Some slides are derived from “ How to Publish Linked Data on the Web” by Chris Bizer, Richard Cyganiak and Tom Heath http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/LinkedDataTutorial/