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RDFa Introductory Course Session 2/4 How RDFa
 

RDFa Introductory Course Session 2/4 How RDFa

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Session 2/4. How RDFa. An introductory one day workshop on RDFa and its relevance, organised and delivered by Netskills.

Session 2/4. How RDFa. An introductory one day workshop on RDFa and its relevance, organised and delivered by Netskills.

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RDFa Introductory Course Session 2/4 How RDFa RDFa Introductory Course Session 2/4 How RDFa Presentation Transcript

  • How RDFa works
  • How does RDFa work Session 2/4
  • An RDFa basics tutorial by Manu Sporny http://www.youtube.com/watch?v=ldl0m-5zLz4&feature=player_embedded
  • Real metadata Resource description framework ‣ RDF is a generic "way" of using definitive metadata with web resources. ‣ RDF describes "things" (entities, defined by uniform resource identifiers, URIs) by assigning properties and corresponding values—statements are known as "triples" consisting of [subject] [predicate] [object]. ‣ The predicate URI usually references a term in a standard metadata vocabulary, resulting in unambiguous meaning. ‣ Any part of the triple can be a URI and URIs can point to other URIs that can be read using HTTP and extended (or related) in other web resources, thus a scalable model and very flexible. http://www.w3.org/TR/rdf-primer/ http://www.w3.org/RDF/
  • RDFa distiller Extract RDF from HTML + RDFa W3C service to identify and list RDF from a web page ‣ using web address, local file or direct text inputs ‣ provides “clean” view of data hierarchy ‣ enables simple check on markup validation *and* intended meaning http://www.w3.org/2007/08/pyRdfa/
  • Distilled RDFa page <?xml version="1.0" encoding="utf-8"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:v="http://rdf.data-vocabulary.org/#" xmlns:xhv="http://www.w3.org/1999/xhtml/vocab#" xmlns:xml="http://www.w3.org/XML/1998/namespace" > <v:Person> <v:nickname>mungeo</v:nickname> <v:address> <v:Address> <v:region>Ulster</v:region> <v:locality>Donegal</v:locality> </v:Address> </v:address> <v:url rdf:resource="http://www.platypusconsultancy.com"/> <v:name>George Munroe</v:name> <v:title>consultant trainer</v:title> <v:affiliation>Netskills</v:affiliation> </v:Person> </rdf:RDF> RDFa
  • Validating the RDF extracted from an RDFa file and exploring the data structure ‣ obtain a tabular description of entity classes and corresponding properties ‣ list inherent RDF triples ‣ visualise relationships with simple graphical representations http://www.w3.org/RDF/Validator/
  • View RDF triples within RDF file RDFa
  • View graph of entities and properties RDFa
  • Practical exercise Extracting RDF from RDFa ‣ open the W3C RDFa distiller service with your web browser ‣ use the “Distill by file upload” option, select your sample RDFa file and “Go!” ‣ view the page source of the output file and note the RDF tagging ‣ copy all of the page source of the output file (RDF) ‣ open the W3C RDF validation service with your web browser ‣ use the “Check by direct input” option and paste in your RDF source ‣ select “Triples and graph” from the “Display result options” section ‣ click the “Parse RDF” button and explore the RDF triples and graph produced by selecting “Grid view” and “SVG graph” ‣ if time permits repeat the above process with the W3C RDF primer sample file (http://www.w3.org/2006/07/SWD/RDFa/primer/alice-example.html) only use the validator directly by selecting the “Check by URI” option and supplying the distiller service address with the sample RDFa file in a query string as follows: http://www.w3.org/2007/08/pyRdfa/extract?uri=http://www.w3.org/2006/07/SWD/ RDFa/primer/alice-example.html
  • Metadata vocabularies The importance of shared metadata Everyone (and every computer) must have a common understanding of what particular entities and properties actually are ‣ concept of XML namespaces, used to make descriptions of entity classes and corresponding properties available via the web ‣ these descriptions supplied as RDF (or RDFa) files with a URL (URI) And there’s more to it than just a flat list of entities and properties ‣ a real understanding involves being aware of the relationships between entity classes as well as what properties are associated with an entity ‣ possibly a very complex “ontology” but built very simply from triples where the object of one triple may be the subject of another RDFa
  • Namespaces These namespaces are used to describe entities in X number of documents Namespaces (819 known namespaces) Number of documents http://xmlns.com/foaf/0.1/ 1,261,416 http://purl.org/goodrelations/v1# 645,210 http://blogs.yandex.ru/schema/foaf/ 584,781 http://www.w3.org/2002/07/owl# 451,113 http://sites.wiwiss.fu-berlin.de/suhl/bi... 252,361 http://rdfs.org/sioc/ns# 183,228 http://www.w3.org/2003/01/geo/wgs84_pos# 157,659 http://rdfs.org/sioc/types# 117,621 http://semantic-mediawiki.org/swivt/1.0# 64,281 http://xmlns.com/foaf/spec/ 50,514 http://pingthesemanticweb.com/
  • Entities The number of each entity type known by pingthesemanticweb.com Entity types (10,500 known entity types) Count http://xmlns.com/foaf/0.1/Person 19,015,352 http://xmlns.com/foaf/0.1/Document 5,115,311 http://purl.org/goodrelations/v1#Product... 1,418,899 http://purl.org/goodrelations/v1#UnitPri... 999,893 http://purl.org/goodrelations/v1#Busines... 753,812 http://purl.org/goodrelations/v1#Offerin... 644,652 http://purl.org/goodrelations/v1#TypeAnd... 626,684 http://blogs.yandex.ru/schema/foaf/Posts 585,188 http://www.w3.org/2002/07/owl#Ontology 446,664 http://purl.org/goodrelations/v1#Product... 374,456 http://pingthesemanticweb.com/
  • Exploring vocabularies Commonly used metadata vocabularies Google (person, organisation, review, event, recipe) ‣ http://rdf.data-vocabulary.org/ FOAF (Friend Of A Friend) ‣ http://xmlns.com/foaf/0.1/ GoodRelations (ecommerce) ‣ http://www.heppnetz.de/ontologies/goodrelations/v1.owl Dublin Core (generic document) ‣ http://dublincore.org/2008/01/14/dcelements.rdf Creative Commons (licensing) ‣ http://creativecommons.org/ns SKOS (Simple Knowledge Organisation System) ‣ http://www.w3.org/2009/08/skos-reference/skos.rdf RDFa
  • Viewing complex vocabularies—ontologies Use the OpenLink Data Explorer extension in Firefox http://ode.openlinksw.com/
  • Exploring vocabularies Digging into metadata vocabularies Use the Firefox browser with OpenLink Data Explorer extension and/ or W3C RDF validator and grapher online service to view the following vocabularies: ‣ Dublin Core at: http://dublincore.org/2008/01/14/dcelements.rdf ‣ GoodRelations at: http://www.heppnetz.de/ontologies/goodrelations/v1.owl Use the pyRdfa distiller service to extract and view the RDF vocabulary information from the following descriptions: ‣ FOAF at: http://xmlns.com/foaf/0.1/ ‣ Creative Commons at: http://creativecommons.org/ns
  • RDFa tools Summary of useful RDFa related tools RDFa distiller (extract pure RDF from HTML + RDFa) ‣ http://www.w3.org/2007/08/pyRdfa/ ‣ get RDF directly from http://example.com/sample.html using single address http://www.w3.org/2007/08/pyRdfa/extract?uri=http://example.com/sample.html RDF validator and grapher ‣ http://www.w3.org/RDF/Validator/ OpenLink Data Explorer extension for Firefox ‣ https://addons.mozilla.org/en-US/firefox/addon/8062 List global namespaces and entities ‣ http://pingthesemanticweb.com/ RDFa