469 talk

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469 talk

  1. 1. RDF/XMLA brief introduction<br />Alison Hunt March 26, 2011<br />for LIS469 XML<br />
  2. 2. RDF/XML is a data format<br />It represents information <br />for a data model <br />called RDF<br />
  3. 3. RDFResource Description Frameworkis a data model<br />It structures metadata <br />for<br />the Semantic Web and<br />the RDA content standard<br />(resource description and access)<br />
  4. 4. RDFdescribes a resource<br />LIS469 Class Blog<br />
  5. 5. A resource has properties<br />creator<br />language<br />LIS469 Class Blog<br />format<br />subject<br />
  6. 6. Properties have values<br />creator<br />language<br />LIS469 Class Blog<br />format<br />subject<br />
  7. 7. RDFdescriptions make statements<br />The LIS469 class blog was created by Aaron Rubinstein.<br />The LIS469 class blog is written in English.<br />The LIS469 class blog is formatted as text/HTML.<br />The LIS469 class blog is about the subject of XML.<br />
  8. 8. RDFstatements are triples<br />Resource<br />Subject<br />LIS469 class blog<br />LIS469 class blog<br />LIS469 class blog<br />LIS469 class blog<br />Property<br />Predicate<br />Creator<br />Language<br />Format<br />Subject<br />Value<br />Object<br />Aaron Rubinstein<br />English<br />Text/HTML<br />XML<br />
  9. 9. RDF statements link two things in one direction.<br />Node<br />LIS469 class blog<br />LIS469 class blog<br />LIS469 class blog<br />LIS469 class blog<br />Arc<br />Creator<br />Language<br />Format<br />Subject<br />Node<br />Aaron Rubinstein<br />English<br />Text/HTML<br />XML<br />
  10. 10. RDF statements link two things in one direction.<br />Properties may have multiple values.<br />RDF has several ways to model this:<br />blank nodes, bags, collections, etc.<br />However, the end result will be a set of triples<br /> which link the subject with each value.<br />
  11. 11. RDF statements require URIs that have meaning for computer applications<br />Resource<br />Must be a URI<br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br />Here, the blog URL replaces its name<br />
  12. 12. RDF Shines<br />By using URIs, <br />RDF can describe things that <br />cannot be located or retrieved on the web.<br />People, institutions, cars, concepts…anything.<br />FRBR works, <br />expressions or manifestations<br />Tiger Lily<br />collective amnesia<br />
  13. 13. RDF statements require URIs for properties<br />Resource<br />Must be a URI<br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br />Property<br />Must be a URI<br /><http://purl.org/dc/elements/1.1/creator><br /><http://purl.org/dc/elements/1.1/language><br /><http://purl.org/dc/elements/1.1/format><br /><http://purl.org/dc/elements/1.1/subject><br />Here, Dublin Core URIs are used for the property<br />
  14. 14. Values can be URIs or literal strings of characters<br />Resource<br />Must be a URI<br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br /><http://lis469.wordpress.com/><br />Property<br />Must be a URI<br /><http://purl.org/dc/elements/1.1/creator><br /><http://purl.org/dc/elements/1.1/language><br /><http://purl.org/dc/elements/1.1/format><br /><http://purl.org/dc/elements/1.1/subject><br />Value<br />Can be URI or literal<br />Aaron Rubinstein<br />English<br />Text/html<br /><http://id.loc.gov/authorities/sh97007825#concept><br />Here, XML is identified by a URI <br />from Library of Congress Subject Headings<br />
  15. 15. RDF graph with URIs<br />Note:<br />RDF graphs show<br />literals in a box<br />URIs in an oval<br />We are using a URI as the value of the subject property.<br />So the graph changes from box to oval.<br />This actually indicates a really significant change…<br /><http://purl.org/dc/elements/1.1/creator><br /><http://purl.org/dc/elements/1.1/language><br /><http://lis469.wordpress.com/><br /><http://purl.org/dc/elements/1.1/format><br /><http://purl.org/dc/elements/1.1/subject><br />
  16. 16. A value with a URI can be the subject of other statements<br /><http://purl.org/dc/elements/1.1/creator><br /><http://purl.org/dc/elements/1.1/language><br /><http://purl.org/dc/elements/1.1/format><br /><http://purl.org/dc/elements/1.1/subject><br />Library <br />of<br />Congress<br /><http://purl.org/dc/elements/1.1/creator><br />
  17. 17. RDF links stuff!<br />
  18. 18. RDF shines<br />It is easy <br />to work across <br />different data sources, types and formats.<br />RDF can link things <br />by tapping massive databases of RDF statements called "triplestores."<br />There are more than 27 billion triples stored now.<br />
  19. 19. RDF/XML is a data format<br />001111000010100010000100010010001111000000000011110000000111111111100000000000111111111110000000000011<br />XML document serializes <br />the RDF graph so it can be<br />processed by computers<br />for storage and transmission<br />
  20. 20. RDF expressed as XML<br />RDF<br />XML<br />Class Blog<br />Creator<br /> Aaron Rubinstein<br />Language<br /> English<br />Format<br /> Text-HTML<br />Subject<br /> XML URI<br />The XML format is closed; it will not link like the RDF graph does.<br />
  21. 21. Starting the RDF/XML file<br />RDF<br />RDF is the root element<br />The rdf: prefix is from the rdf namespace<br />We are also using Dublin Core elements<br />XML<br /><?xml version="1.0"?><br /><rdf:RDF<br />xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#<br />xmlns:dc=http://purl.org/dc/elements/1.1/><br />
  22. 22. Where is the resource named?<br />RDF<br />Each resource being described is tagged with the RDF element <description><br />The about attribute spells out the URI<br />Of the resource that is the subject of the RDF statement<br />XML<br /><?xml version="1.0"?><br /><rdf:RDF<br />xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#<br />xmlns:dc=http://purl.org/dc/elements/1.1/><br /><rdf:Description<br />Rdf:about="http://lis469.wordpress.com/"><br />
  23. 23. Properties and values?<br />RDF<br />Properties become child elements of Description.<br />They appear as tags.<br />Literal RDF values become the value of those child elements, between opening and closing tags.<br />When RDF values are expressed as URIs, <br />they become an attribute, called "resource,"<br /> of the child element.<br />XML<br /><?xml version="1.0"?><br /><rdf:RDF<br />xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#<br />xmlns:dc=http://purl.org/dc/elements/1.1/><br /><rdf:Description<br />Rdf:about="http://lis469.wordpress.com/"><br /><dc:creator>Aaron Rubinstein</dc:creator><br /><dc:language>English</dc:language><br /><dc:format>text/HTML</dc:format><br /><dc:subjectrdf:resource=" http://id.loc.gov/authorities/sh97007825#concept "/><br /></rdf:Description><br /></rdf:RDF><br />
  24. 24. But properties should be URIs!<br />Namespace declarations generate full URIs <br />for each property<br />dc: is equivalent to http://purl.org/dc/elements/1.1/<br /><dc:format>text/HTML</dc:format><br />is processed as<br /><http://purl.org/dc/elements/1.1/ format> text/HTML </ <http://purl.org/dc/elements/1.1/ format><br />
  25. 25. RDF expressed as XML<br />RDF<br />XML<br /><?xml version="1.0"?><br /><rdf:RDF<br />xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns#<br />xmlns:dc=http://purl.org/dc/elements/1.1/><br /><rdf:Description<br />Rdf:about="http://lis469.wordpress.com/"><br /><dc:creator>Aaron Rubinstein</dc:creator><br /><dc:language>English</dc:language><br /><dc:format>text/HTML</dc:format><br /><dc:subjectrdf:resource=" http://id.loc.gov/authorities/sh97007825#concept "/><br /></rdf:Description><br /></rdf:RDF><br />
  26. 26. RDF/XML is not the only choice<br />PROS<br />RDF/XML is the syntax primarily <br />used by the W3C from the start<br />It plays well with the family of XML technologies.<br />XML uses namespaces and can tag (i.e. express RDF properties) with ultimate flexibility.<br />CONS<br />RDF/XML files are hard for people to read.<br />Namespaces don't always behave the way we expect<br />Most of the developers who have to actually generate linked data find RDF/XML clunky <br />RDF/XML obscures triples <br />
  27. 27. Other RDF data formats are<br />RDFa<br />Embeds RDF metadata in html. Part of Drupal7.<br />TURTLE<br />Very easy for people to read. Preserves RDF triples.<br />JSON<br />Supported by major web applications like JavaScript,<br />so easy to process and familiar to developer community. <br />
  28. 28. You should know<br />W3C is overhauling its RDF recommendations<br />http://www.w3.org/2011/01/rdf-wg-charter<br />You can create your own personal URI<br />http://www.foaf-project.org/<br />For a great overview, skim the new e-book<br />Linked Data: Evolving the Web into a Global Data Space<br />http://linkeddatabook.com/editions/1.0<br />DBPedia is the hub of RDF-linked data<br />http://dbpedia.org/About<br />
  29. 29. The Linked World<br />Linking Open Data cloud diagram, by Richard Cyganiak and AnjaJentzsch. http://lod-cloud.net/<br />

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