Publishing Linked Data

Juan F. SequedaSemantic Technology Conference

June 2011

Thanks Heath & Bizer

Static RDF Files

• Small amount of data (personal FOAF file)• Use RDF/XML because it is the most common

serialization• Save as a .rdf file and upload it to your webserver– http://www.cs.utexas.edu/~jsequeda/foaf.rdf– http://www.cs.utexas.edu/~jsequeda/foaf.rdf#me

• Configure MIME Types– AddType application/rdf+xml .rdf– AddType text/n3;charset=utf-8 .n3

• Make RDF Discoverable from HTML– <link rel="alternate" type="application/rdf+xml" href="company.rdf">

RDF Embedded in HTML Files

• Use RDFa• RDFa is useful when you have template HTML

pages– Can get complicated if your HTML is complicated

• Drupal 7 will do this out of the box

Links to other URIs

<span rel="foaf:interest"><a href="http://dbpedia.org/resource/Database"

property="dcterms:title">Database</a>, <a href="http://dbpedia.org/resource/Data_integration" property="dcterms:title">Data Integration</a>, <a href="http://dbpedia.org/resource/Semantic_Web" property="dcterms:title">Semantic Web</a>, <a href="http://dbpedia.org/resource/Linked_Data" property="dcterms:title">Linked Data</a>, etc.</span>

Linked Data from Relational Databases

• Majority of the data on the web is stored in relational databases

• Enterprises are full of relational databases• Use RDF as common data format for data

integration– RDB2RDF tools expose relational data as RDF

RDB2RDF Systems• D2R Server

– http://www4.wiwiss.fu-berlin.de/bizer/d2rq/– Free University of Berlin– D2RQ Mapping Language

• Virtuoso RDF Views– http://virtuoso.openlinksw.com/dataspace/dav/wiki/Main/VOSSQLRDF– Openlink– Proprietary mapping language

• Triplify– http://triplify.org/Overview– Universitaet Leipzig– SQL/PHP

RDB2RDF Systems

• SquirrelRDF– http://jena.sourceforge.net/SquirrelRDF/– Last update: 2006

• R2O– UPM– http://mayor2.dia.fi.upm.es/oeg-upm/index.php/en/

downloads/9-r2o-odempaster– R2O mapping language– Doesn’t support SPARQL (yet)

• Survey Jan 2009– http://www.w3.org/2005/Incubator/rdb2rdf/

RDB2RDF_SurveyReport.pdf

RDB2RDF Systems

• Spyder– http://www.revelytix.com/content/spyder– Revelytix– W3C RDB2RDF R2RML standard

• Ultrawrap– http://ribs.csres.utexas.edu/ultrawrap/– University of Texas at Austin– W3C RDB2RDF Direct Mapping standard

Current State-of-Art

• W3C RDB2RDF Working Group is generating two standards:– R2RML: RDB to RDF Mapping Language

• Customized mapping

– A Direct Mapping of Relational Data to RDF• Default mapping

• Spyder and Ultrawrap are the only systems that follow the standard

• Benchmarks comparing RDB2RDF systems with native relational database show that RDB2RDF are slow and need a lot more optimization– Ultrawrap performance is almost equal to native SQL

Linked Data from Triplestores• Commercial

– Oracle– Garlik – 4store– Systap – BigData– Ontotext – BigOwlim– Openlink – Virtuoso– Franz – AllegroGraph– Ontobroker - Ontoprise– …

• Open Source– Jena– Sesame– Mulgara– …

• Pubby – Linked Data frontend for SPARQL endpoints– http://www4.wiwiss.fu-berlin.de/pubby/

Linked Data in the Cloud

• Kasabi (Talis)– beta.kasabi.com

• Dydra – dydra.com

• …

Linked Data from APIs

• http://www4.wiwiss.fu-berlin.de/bizer/bookmashup/• http://www4.wiwiss.fu-berlin.de/flickrwrappr/ • Assign HTTP URIs to resources that the API provides• When a URI is dereferenced, rewrite client request to

a request against the API– Different types of query and retrieval interfaces

• Result of the API are transformed to RDF and sent back to the client– Different return formats: XML, JSON, ATOM

Testing your Linked Data• Vapour Linked Data Validator

– http://idi.fundacionctic.org/vapour• RDF:Alerts

– http://swse.deri.org/RDFAlerts/• Sindice Inspector

– http://inspector.sindice.com/• cURL

– http://richard.cyganiak.de/blog/2007/02/debugging-semantic-web-sites-with-curl/

• Firefox Plugins– Live HTTP Headers

https://addons.mozilla.org/af/firefox/addon/live-http-headers/– Modify Headers

https://addons.mozilla.org/af/firefox/addon/modify-headers/• Linked Data browsers

– http://browse.semanticweb.org/