XR Tutorial

Start flooding the world with RDF data

Last Update

10/16/2005; 1:29:31 AM

Try XHTML 2.0 Src XHTML 2.0 RDF Metadata

Introduction

The tutorial will first show how to create RDF in this format, and then show how to adapt the static RDF to an XML to RDF transformation by adding XPath expressions.

Creating RDF data

Resources have properties. The following example shows that the resource at URI http://www.w3.org/ has a dc:title property with value "World Wide Web Consortium".

<xr:transform xmlns:xr="https://w3future.com/xr/ns/" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:h="http://www.w3.org/1999/xhtml"> <xr:introducing> <rdfs:Resource xr:uri="http://www.w3.org/"> <dc:title>World Wide Web Consortium</dc:title> </rdfs:Resource> </xr:introducing> </xr:transform>

A property value can also be another resource. http://www.w3.org/ also has a dc:rights property. The value of this property is another resource. This resource also has it's own dc:title property. (I'll leave out the root element from now on, it's the same every time.)

<xr:introducing> <rdfs:Resource xr:uri="http://www.w3.org/"> <dc:title>World Wide Web Consortium</dc:title> <dc:rights> <rdfs:Resource xr:uri="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"> <dc:title>IPR Notice and Disclaimers</dc:title> </rdfs:Resource> </dc:rights> </rdfs:Resource> </xr:introducing>

Transforming

Now we'll do the above for all xhtml documents. Let's first create a transformation that extracts the title. The static information from the first example above will be replaced by xpaths.

The xr:uri attribute is replaced by a xr:uriSelect attribute. The xpath expression for the URI is $documentURI, which is the URI of the document being transformed.
The text content of the dc:title property is replaced by a xr:select attribute. The xpath expression selects the title element of the xhtml file.

<xr:introducing> <rdfs:Resource xr:uriSelect="$documentURI"> <dc:title xr:select="/h:html/h:head/h:title" /> </rdfs:Resource> </xr:introducing>

The dc:rights property can be extracted from xhtml documents by looking for <a> elements with a rel='Copyright' attribute. So the xpath for the dc:rights property is //h:a[@rel='Copyright']. The URI for the copyright webpage is in the href attribute. The title from that webpage can then be looked up by selecting the title element and using the document() function from XSLT.

<xr:introducing> <rdfs:Resource xr:uriSelect="$documentURI"> <dc:title xr:select="/h:html/h:head/h:title" /> <dc:rights xr:select="//h:a[@rel='Copyright']"> <rdfs:Resource xr:uriSelect="@href"> <dc:title xr:select="document(@href)/h:html/h:head/h:title" /> </rdfs:Resource> </dc:rights> </rdfs:Resource> </xr:introducing>

Instead of transforming the copyright webpage in the dc:rights element, it can also be separated. This is usually more readable, and it is preferred when several properties point to the same resource.

<xr:introducing> <rdfs:Resource xr:uriSelect="$documentURI"> <dc:title xr:select="/h:html/h:head/h:title" /> <dc:rights xr:select="//h:a[@rel='Copyright']" /> </rdfs:Resource> </xr:introducing> <xr:introducing xr:select="//h:a[@rel='Copyright']"> <rdfs:Resource xr:uriSelect="@href"> <dc:title xr:select="document(@href)/h:html/h:head/h:title" /> </rdfs:Resource> </xr:introducing>