Resource Description Framework

Release: 2008-01-27
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RDF/XML

Resource Description Framework (RDF) is the industry standard in describing and exchanging information about anything in the world of the Internet. The RDF concept is structured in 'triples': subject, predicate and object.

A subject is the thing you are describing – a webpage, an image, a contact, a person in a company. Its predicate is the type of fact you are particularly describing – file size, colour, name, age, title, URI. The object is the actual value of the predicate – '26KiloBytes', 'Midnight Blue', 'San Qwe', '902', 'Articles of Storan', 'http://articles.nowhere.com.bc/storan_home.xhtml#section1268'.

RDF can be displayed in a number of formats including a visual graph, a procedural language or even markup. One of the common formats is using an XML structure called RDF/XML.

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE rdf:RDF [

  <!ENTITY xs "http:www.w3.org/2001/XMLSchema#">

  <!ENTITY zt "http://test.examples.org/terms#">
 
]>

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:z="http://test.examples.org/metadata">

  <rdf:Description rdf:about="http://articles.nowhere.com.bc/storan_home.xhtml#section1268">

    <z:author rdf:resource="#author"/>

    <z:filesize rdf:datatype="&zt;electronicSize">26KiloBytes</z:filesize>

    <z:title rdf:datatype="&xs;string">Articles of Storan</z:title>

    <z:categoryColour rdf:datatype="&zt;colour">Midnight Blue</z:categoryColour>

  </rdf:Description>



  <rdf:Description rdf:ID="author">

    <z:givenName>San</z:givenName>

    <z:familyName>Qwe</z:familyName>

    <z:age>902</z:age>

  </rdf:Description>

</rdf:RDF>

The RDF/XML document above describes the 1268th section of the webpage at http://articles.nowhere.com.bc/storan_home.xhtml (the subject). Stating its author, filesize, title and category colour (predicates). The rdf:type attribute states the character restrictions of the value (object). The author refers to another description that is all about the author (uniquely identified just by author)(subject) and stating the given name, family name and age (predicates).

As you can see RDF is just the framework and any other XML structure can be used for the predicates as long as they are bound to an XML Namespace. Resource Description Framework is mostly used for storing and sharing metadata (data about data) but is also used for program preferences, manifests and database formats. RDF Documents tend to have a .rdf file extension and have the MIME Type of 'application/rdf+xml'.

Dublin Core

A common set of predicates are provided from Dublin Core Elements 1.1 with the namespace 'http://purl.org/dc/elements/1.1/' and usually the prefix 'dc'. Such predicates include title, creator, description, publisher, contributor, language (such as en-GB) and rights (copyrights information).

RSS News Feeds

RSS 1.0, Really Simple Syndication or RDF Site Summary, is a news feed format using Resource Description Framework as its host document. RSS was originally developed by Userland at version 0.90, and used in Netscape 4's news portal, using the RDF language of the time. Then Userland decided to make it into a lone language in 0.91 to 0.94.

These versions are now obsoleted by the RSS-DEV's RSS 1.0 bringing it back to its roots with the RDF of today. UserLand also updated their format, but as version 1.0 was already taken they chose to call it RSS 2.0. So RSS 2.0 is not an improved version of RSS 1.0 but both 1.0 and 2.0 are two competing formats that both are used today. Plus Atom is another site summary or news feed format. Most RSS Readers support all formats. Here, we are talking about RSS 1.0 only as it is the only RSS format that uses the existing industry metadata standard of RDF.

These documents can use the RDF extension and MIME Type or the unofficial .rss file extension and the 'application/rss+xml' MIME Type which is more detectable by browsers that can auto-discover an RSS Feed on a webpage. Such browsers include Mozilla Firefox 1.5+, Opera 7(.2 i think)+, Apple Safari 2.0+ and Microsoft Internet Explorer 7+.

You can subscribe to these RSS Feeds which provide latest news or blog entries or other headline related information. You can drag or copy and paste the RSS Feed's URI to a dedicated RSS Reader or Aggregator. As it is only XML they are quick to download and the appearance of the information is handled by the browser or RSS Feed reader and can usually be customized. Feeds are used so people can be notified by any changes or updates right in their browser, plugin, email client or other RSS supporting program without searching on the actual website. These feeds will have a link to the full information on the actual webpage if there is just a headline or summary.

<?xml version="1.0" encoding="UTF-8"?>

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://purl.org/rss/1.0/" xmlns:dc="http://purl.org/dc/elements/1.1/" xml:lang="en">

  <channel rdf:about="http://rss.example.co.uk/">

    <title>Web News</title>

    <link>http://rss.example.co.uk/</link>

    <description>Web related news topics</description>

    <image rdf:resource="http://www.example.co.uk/images/webit.png"/>

    <dc:language>en-GB</dc:language>

    <items>

      <rdf:Seq>

        <rdf:li rdf:resource="http://www.getthunderbird.com/"/>

        <rdf:li rdf:resource="http://www.getfirefox.com/"/>

        <rdf:li rdf:resource="http://www.opera.com/"/>

      </rdf:Seq>

    </items>

  </channel>

  <image rdf:about="http://www.exmple.co.uk/images/webit.png">

    <title>Webbed logo</title>

    <link>http://www.example.co.uk</link>

    <url>http://www.example.co.uk/images/webit.png</url>

  </image>

  <item rdf:about="http://www.getthunderbird.com/">

    <title>Email Watch: Mozilla Thunderbird 2.0.0.6 released</title>

    <link>http://www.getthunderbird.com/</link>

    <description>If you have Mozilla Thunderbird 1.5 or higher you can go to Help - Check For Updates to update your copy. Otherwise the 2.0.0.6 version is available from the Moziila Thunderbird site.</description>

    <dc:date>2007-08-02T14:10:00+00:00</dc:date>

  </item>

  <item rdf:about="http://www.getfirefox.com/">

    <title>Browser Watch: Mozilla Firefox 2.0.0.6 released</title>

    <link>http://www.getfirefox.com/</link>

    <description>If you have Mozilla Firefox 1.5 or higher you can go to Help - Check For Updates to update your copy. Otherwise the 2.0.0.6 version is available from the Moziila Firefox Site.</description>

    <dc:date>2007-07-31T19:50:00+00:00</dc:date>

  </item>

  <item rdf:about="http://www.opera.com/">

    <title>Browser Watch: Opera 9.22 has been released</title>

    <link>http://www.opera.com/</link>

    <description>Opera 9 supports XML 1.1, XSLT & XPath, Canvas, saved sessions, Widgets, per-site preferences and is one of the first web browsers to support all of DOM 2.</description>
    <dc:date>2007-07-29T14:30:00+00:00</dc:date>

  </item>

</rdf:RDF>

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Interesting Links for Web Standards Articles

Depreciated but archived:

Legend Scrolls

Resource Description Framework

RDF/XML

Dublin Core

RSS News Feeds

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