How RDFa works
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RDFa is a method for embedding Rich Data Formats metadata within HTML documents. It allows metadata like titles, descriptions and URLs to be added to HTML pages in a way that is readable both by humans and machines. The summary describes how RDFa works by defining things with URIs and assigning them properties and values as triples. It also mentions the RDFa distiller tool that can extract the RDF metadata from HTML pages marked up with RDFa.
![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/](https://image.slidesharecdn.com/howrdfaworks-100426110555-phpapp02/85/How-RDFa-works-4-320.jpg)
How RDFa works
- 2. How does RDFa work Session 2/4
- 3. An RDFa basics tutorial by Manu Sporny http://www.youtube.com/watch?v=ldl0m-5zLz4&feature=player_embedded
- 4. 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/
- 5. 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/
- 6. 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
- 7. 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/
- 8. View RDF triples within RDF file RDFa
- 9. View graph of entities and properties RDFa
- 10. 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
- 11. 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
- 12. 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/
- 13. 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/
- 14. 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
- 15. Viewing complex vocabularies—ontologies Use the OpenLink Data Explorer extension in Firefox http://ode.openlinksw.com/
- 22. 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
- 23. 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