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RDF: Data Description

RDF: Data Description. With HTML, the Web is for reading With XML, the Web is for processing Necessary to know who wrote this? who owns it? who authorised it? when is it valid? what rights are ascribed to it?. RDF: Metadata. Data about data information about documents

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RDF: Data Description

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  1. RDF: Data Description • With HTML, the Web is for reading • With XML, the Web is for processing • Necessary to know • who wrote this? • who owns it? • who authorised it? • when is it valid? • what rights are ascribed to it?

  2. RDF: Metadata • Data about data • information about documents • title, author, journal, date, keywords • information about people • role, history, salary, expertise • information about exhibits • catalogue number, price, date, artist • information about metadata • validity, purpose, compiler, authority

  3. Blue Mountain Content: Some hills, a lake and the sun Width Height Represents: peace tranquility Artist Title Types of Metadata • Catalogue information: artist, title, date acquired, size. • Syntactic content: colour, texture and shapes. • Semantic content: landscape or happiness.

  4. Standards for Metadata • What do you put in the metadata? • What is the syntax? • What is the semantics? • Where does the metadata go?

  5. RDF: Data Description • Simple semantic network • resources • properties • values • Schemas • Statements • Triples

  6. RDF Model http://www.w3c.org/Intro.html Author Tim Berners-Lee

  7. RDF Model http://www.w3c.org/Intro.html predicate Author subject Tim Berners-Lee object

  8. http://www.w3c.org/Intro.html predicate subject author object email name tbl@w3c.org Tim Berners-Lee RDF Model

  9. RDF Syntax <?xml version="1.0"?> <RDF> <Description about="http://www.ecs.soton.ac.uk/~lac"> …put some metadata in here!... </Description> </RDF> • But RDF doesn't know about any metadata!

  10. RDF Descriptions • Someone has to invent schemes for describing things • Schemas, ontologies, terminologies… • External authorities • Every term represented by URI • e.g.http://purl.oclc.org/dc#Title • use XML namespace to abbreviate • applies semantics and disambiguates

  11. RDF Descriptions • The title is "Trailblazing the literature" <Title> Trailblazing the literature </Title> • Who defines the title? Dublin Core! XML NamespaceDC= http://purl.oclc.org/dc# <DC:Title>Trailblazing the literature</DC:Title>

  12. Simple RDF Example <?xml version="1.0"?> <RDF xmlns:DC="http://elib.jisc.ac.uk/dublincore#" > <Description about="http://www.ecs.soton.ac.uk/~lac/ht99.pdf"> <DC:Title>Trailblazing the literature</DC:Title> </Description> </RDF> RDF has its own namespace which is not shown here. You really need to add the following to the RDF element xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#" NB

  13. Simple RDF Example <?xml version="1.0"?> <RDF xmlns:DC="http://elib.jisc.ac.uk/dublincore#" > <Description about="http://www.ecs.soton.ac.uk/~lac/ht99.pdf"> <DC:Title>Trailblazing the literature</DC:Title> <DC:Creator>Leslie Carr</DC:Creator> </Description> </RDF>

  14. Simple RDF Example String <?xml version="1.0"?> <RDF xmlns:DC="http://elib.jisc.ac.uk/dublincore#" > <Description about="http://www.ecs.soton.ac.uk/~lac/ht99.pdf"> <DC:Title>Trailblazing the literature</DC:Title> <DC:Creator resource="http://www.ecs.soton.ac.uk/~lac" /> </Description> </RDF> AnotherResource Use this RDF to get youstarted in the exercises!

  15. RDF Collections • The students in course 6.001 are Amy, Tim, John, Mary, and Sue. • RDF provides • bag • sequence • alternative

  16. Why RDF? • But why yet another standard? • Any form of data can be modelled in plain XML. These slides are adapted from Tim Berners-Lee's Roadmap to the Semantic Web available at http://www.w3.org/DesignIssues/RDF-XML.html

  17. RDF vs XML • example RDF assertion • "The author of this page is Les". • triple(page, author, "Les") http://www.soton.ac.uk/~lac/XMLcourseSession6.ppt#slide19 author Les

  18. RDF vs XML • How would this information be typically be represented in XML? <author> <uri>http://...</uri> <name>Les</name> </author> • or <document href="http://..."> <author>Les</author> </document>

  19. RDF vs XML • or <document> <author> <uri>href="http://..."</uri> <details> <name>Les</name> </details> </author> </document> • or just <document href="http://..." author="Les" />

  20. RDF vs XML • They all seem the same • because we understand the tags • But how about these? <stuff> <x> <wotzit a="foo"/> <z> <thingy>bar</thingy> </z> </x> </stuff> <stuff> <thingy>bar</thingy> <x> <wotzit>foo</wotzit> </x> </stuff>

  21. RDF vs XML • Is a foo a thingy of a bar? • Or bar a wotzit of a foo? • There are grammatical questions we can ask of the XML structure… • e.g. does the x element contain a wotzit • …but not semantic ones • Because no XML semantics are defined

  22. RDF vs XML • IF a schema is defined • AND IF the schema limits the number of ways of making the same statement • THEN the questions • does x have a child foo with attribute a and value foo • who is the author of page • MAY BE similar

  23. RDF Schema • Standard to extend RDF statements • via types, classes, inheritance • Les is the author of this book • An author is a type of person • A book is an item of merchandise • Allows much richer sets of inferences

  24. RDF Deployment • Information can be "added" to itemsby a third party • Information may be distributed • professional associations, • qualification authorities • reviewers, portal authorities • Agent architecture • resolve conflicting claims

  25. RDF Deployment • Options for locating the metadata

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