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Using JavaScript in Linked Data Applications

Using JavaScript in Linked Data Applications. Oshani Seneviratne Oct 12, 2010. Why HTML and Javascript ?. It would: Make the application available widely, almost universally Allow the application to be delivered over HTTP

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Using JavaScript in Linked Data Applications

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  1. Using JavaScript in Linked Data Applications Oshani Seneviratne Oct 12, 2010

  2. Why HTML and Javascript? • It would: • Make the application available widely, almost universally • Allow the application to be delivered over HTTP • Run in the browser thus making use of the existing client side cache • Provide all the UI elements we need very easily

  3. Javascript Libraries • Rdflib + Widget Library • Written by Tabulator developers • Can be used to create user interfaces that use Semantic Web Data • Download from:http://dig.csail.mit.edu/2010/rdf-widgets/download.html • RDFQuery • Written by JeniTennison et al • Can be used to parse RDFa, query over facts and reason to produce more facts • Depends on jQuery • Download from:http://code.google.com/p/rdfquery • More Javascript libraries are available at: http://esw.w3.org/SemanticWebTools#JavaScript_Developers

  4. Same Origin Policy • Rule enforced in browsers for security • Javascript code running on a webpage cannot access any resources from other domains

  5. But there are some workarounds • You can: • Run your code in a trusted environment (standalone app, iPhone app, browser, browser extension, greasemonkey script) • Use a “proxy” server • Use browsers that support CORS (Firefox 3.5, Safari 4). However, the servers have to accept the headers sent by the browsers. • Use JSONP (JSON with Padding)

  6. Our Solution • Use a proxy server to provide JSONP translation of data available at any location on the Web. • TalisMetamorph web service (http://convert.test.talis.com) allows for converting between different RDF syntaxes • JSONP output format is available from the Metamorph service • Cross domain transfer of JSON is supported natively in libraries like jQuery

  7. Our Task • Look up a FOAF URI • Extract that person’s friends • Look at the friends’ FOAF files • See where they work • Use the workplace URI to query dbpedia for it’s location • Print a list of Tim’s friends, their workplaces and where the workplaces are located

  8. 1 Look up Tim’s FOAF URI varurl = 'http://convert.test.talis.com/?data-uri[]=http://www.w3.org/People/Berners-Lee/card#i&input=&output=jsonp&callback=?'; $.getJSON(url, function(data){ //Do something with the data });

  9. 2 Extract his friends vartim = "http://www.w3.org/People/Berners-Lee/card#i" var FOAF_KNOWS = “http://xmlns.com/foaf/0.1/knows” $.each(data[tim][”FOAF_KNOWS"], function{ //Process the friend data here. });

  10. 3 Look at the friends’ FOAF files • Same as 1. Use the metamorph service to load all the data of Tim’s friends. varurl = 'http://convert.test.talis.com/?data-uri[]=<friend_uri>&input=&output=jsonp&callback=?'; $.getJSON(url, function(data){ //Do something with the data });

  11. 4 See where the friends work var WOKPLACE_HOMEPAGE = "http://xmlns.com/foaf/0.1/workplaceHomepage"; friend.workplaceHomepage= friend_data[friend.id][WOKPLACE_HOMEPAGE][0].value;

  12. 5 Query DBpedia PREFIX prop: <http://dbpedia.org/property/> PREFIX ont: <http://dbpedia.org/ontology/> PREFIX foaf: <http://xmlns/foaf/0.1/> PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> SELECT DISTINCT ?label ?lat ?long WHERE { { {?resource prop:website <website_url> .} UNION{?resource foaf:homepage <website_url>.} } { {?resource ont:location ?location. OPTIONAL { ?location geo:lat ?lat. ?location geo:long ?long.} OPTIONAL {?location rdfs:label ?label.} } UNION {?subject prop:employer ?resource} UNION {?subject prop:institution ?resource} UNION {?subject prop:workInstitution ?resource} UNION {?subject prop:workInstitutions ?resource} UNION {?subject prop:workplaces ?resource} UNION {?subject ont:occupation ?resource} OPTIONAL { ?resource geo:lat ?lat. ?resource geo:long ?long.} OPTIONAL {?resource rdfs:label ?label.}} FILTER langMatches( lang(?label), 'en')}

  13. 5.1 Sending the Query to dbpedia "http://dbpedia.org/sparql? default-graph-uri=http://dbpedia.org& should-sponge=soft& query=*query_goes_in_here*& format=application/json& callback=?"

  14. Demo • Available at: • http://dig.csail.mit.edu/2010/Courses/6.898/SWLibraries/javascript/demo/

  15. Tools that are helpful in debugging • Firebug • https://addons.mozilla.org/en-US/firefox/addon/1843 • JSON formatter • http://jsonformatter.curiousconcept.com/

  16. Quiz • Tim has alternate URIs specified in his FOAF file at http://www.w3.org/People/Berners-Lee/card#i. How can you modify this code to look up the workplaces of friends specified in those FOAF uris as well? • How do you find whether people in Tim’s FOAF file are in the same group (foaf:group) as Tim?

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