1. RDF/XMLA brief introduction Alison Hunt March 26, 2011 for LIS469 XML

2. RDF/XML is a data format It represents information for a data model called RDF

3. RDFResource Description Frameworkis a data model It structures metadata for the Semantic Web and the RDA content standard (resource description and access)

4. RDFdescribes a resource LIS469 Class Blog

5. A resource has properties creator language LIS469 Class Blog format subject

6. Properties have values creator language LIS469 Class Blog format subject

7. RDFdescriptions make statements The LIS469 class blog was created by Aaron Rubinstein. The LIS469 class blog is written in English. The LIS469 class blog is formatted as text/HTML. The LIS469 class blog is about the subject of XML.

8. RDFstatements are triples Resource Subject LIS469 class blog LIS469 class blog LIS469 class blog LIS469 class blog Property Predicate Creator Language Format Subject Value Object Aaron Rubinstein English Text/HTML XML

9. RDF statements link two things in one direction. Node LIS469 class blog LIS469 class blog LIS469 class blog LIS469 class blog Arc Creator Language Format Subject Node Aaron Rubinstein English Text/HTML XML

10. RDF statements link two things in one direction. Properties may have multiple values. RDF has several ways to model this: blank nodes, bags, collections, etc. However, the end result will be a set of triples which link the subject with each value.

11. RDF statements require URIs that have meaning for computer applications Resource Must be a URI <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> Here, the blog URL replaces its name

12. RDF Shines By using URIs, RDF can describe things that cannot be located or retrieved on the web. People, institutions, cars, concepts…anything. FRBR works, expressions or manifestations Tiger Lily collective amnesia

13. RDF statements require URIs for properties Resource Must be a URI <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> Property Must be a URI <http://purl.org/dc/elements/1.1/creator> <http://purl.org/dc/elements/1.1/language> <http://purl.org/dc/elements/1.1/format> <http://purl.org/dc/elements/1.1/subject> Here, Dublin Core URIs are used for the property

14. Values can be URIs or literal strings of characters Resource Must be a URI <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> <http://lis469.wordpress.com/> Property Must be a URI <http://purl.org/dc/elements/1.1/creator> <http://purl.org/dc/elements/1.1/language> <http://purl.org/dc/elements/1.1/format> <http://purl.org/dc/elements/1.1/subject> Value Can be URI or literal Aaron Rubinstein English Text/html <http://id.loc.gov/authorities/sh97007825#concept> Here, XML is identified by a URI from Library of Congress Subject Headings

15. RDF graph with URIs Note: RDF graphs show literals in a box URIs in an oval We are using a URI as the value of the subject property. So the graph changes from box to oval. This actually indicates a really significant change… <http://purl.org/dc/elements/1.1/creator> <http://purl.org/dc/elements/1.1/language> <http://lis469.wordpress.com/> <http://purl.org/dc/elements/1.1/format> <http://purl.org/dc/elements/1.1/subject>

16. A value with a URI can be the subject of other statements <http://purl.org/dc/elements/1.1/creator> <http://purl.org/dc/elements/1.1/language> <http://purl.org/dc/elements/1.1/format> <http://purl.org/dc/elements/1.1/subject> Library of Congress <http://purl.org/dc/elements/1.1/creator>

17. RDF links stuff!

18. RDF shines It is easy to work across different data sources, types and formats. RDF can link things by tapping massive databases of RDF statements called "triplestores." There are more than 27 billion triples stored now.

19. RDF/XML is a data format 001111000010100010000100010010001111000000000011110000000111111111100000000000111111111110000000000011 XML document serializes the RDF graph so it can be processed by computers for storage and transmission

20. RDF expressed as XML RDF XML Class Blog Creator Aaron Rubinstein Language English Format Text-HTML Subject XML URI The XML format is closed; it will not link like the RDF graph does.

21. Starting the RDF/XML file RDF RDF is the root element The rdf: prefix is from the rdf namespace We are also using Dublin Core elements XML <?xml version="1.0"?> <rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:dc=http://purl.org/dc/elements/1.1/>

22. Where is the resource named? RDF Each resource being described is tagged with the RDF element <description> The about attribute spells out the URI Of the resource that is the subject of the RDF statement XML <?xml version="1.0"?> <rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:dc=http://purl.org/dc/elements/1.1/> <rdf:Description Rdf:about="http://lis469.wordpress.com/">

23. Properties and values? RDF Properties become child elements of Description. They appear as tags. Literal RDF values become the value of those child elements, between opening and closing tags. When RDF values are expressed as URIs, they become an attribute, called "resource," of the child element. XML <?xml version="1.0"?> <rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:dc=http://purl.org/dc/elements/1.1/> <rdf:Description Rdf:about="http://lis469.wordpress.com/"> <dc:creator>Aaron Rubinstein</dc:creator> <dc:language>English</dc:language> <dc:format>text/HTML</dc:format> <dc:subjectrdf:resource=" http://id.loc.gov/authorities/sh97007825#concept "/> </rdf:Description> </rdf:RDF>

24. But properties should be URIs! Namespace declarations generate full URIs for each property dc: is equivalent to http://purl.org/dc/elements/1.1/ <dc:format>text/HTML</dc:format> is processed as <http://purl.org/dc/elements/1.1/ format> text/HTML </ <http://purl.org/dc/elements/1.1/ format>

25. RDF expressed as XML RDF XML <?xml version="1.0"?> <rdf:RDF xmlns:rdf=http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:dc=http://purl.org/dc/elements/1.1/> <rdf:Description Rdf:about="http://lis469.wordpress.com/"> <dc:creator>Aaron Rubinstein</dc:creator> <dc:language>English</dc:language> <dc:format>text/HTML</dc:format> <dc:subjectrdf:resource=" http://id.loc.gov/authorities/sh97007825#concept "/> </rdf:Description> </rdf:RDF>

26. RDF/XML is not the only choice PROS RDF/XML is the syntax primarily used by the W3C from the start It plays well with the family of XML technologies. XML uses namespaces and can tag (i.e. express RDF properties) with ultimate flexibility. CONS RDF/XML files are hard for people to read. Namespaces don't always behave the way we expect Most of the developers who have to actually generate linked data find RDF/XML clunky RDF/XML obscures triples

27. Other RDF data formats are RDFa Embeds RDF metadata in html. Part of Drupal7. TURTLE Very easy for people to read. Preserves RDF triples. JSON Supported by major web applications like JavaScript, so easy to process and familiar to developer community.

28. You should know W3C is overhauling its RDF recommendations http://www.w3.org/2011/01/rdf-wg-charter You can create your own personal URI http://www.foaf-project.org/ For a great overview, skim the new e-book Linked Data: Evolving the Web into a Global Data Space http://linkeddatabook.com/editions/1.0 DBPedia is the hub of RDF-linked data http://dbpedia.org/About

29. The Linked World Linking Open Data cloud diagram, by Richard Cyganiak and AnjaJentzsch. http://lod-cloud.net/