GRDDL


GRDDL is a markup format for Gleaning Resource Descriptions from Dialects of Languages. It is a W3C Recommendation, and enables users to obtain RDF triples out of XML documents, including XHTML. The GRDDL specification shows examples using XSLT, however it was intended to be abstract enough to allow for other implementations as well. It became a Recommendation on September 11, 2007.

Mechanism

XHTML and transformations

A document specifies associated transformations, using one of a number of ways.
For instance, an XHTML document may contain the following markup:

http://dublincore.org/documents/dcq-html/
http://gmpg.org/xfn/11">


Document consumers are informed that there are GRDDL transformations available in this page, by including the following in the profile attribute of the head element:

http://www.w3.org/2003/g/data-view

The available transformations are revealed through one or more link elements:



This code is valid for XHTML 1.x only. The profile attribute has been dropped in HTML5, including its XML serialisation.

Microformats and profile transformations

If an XHTML page contains Microformats, there is usually a specific profile.
For instance, a document with hcard information should have:



When fetched http://www.w3.org/2006/03/hcard has:



and

Use of this profile licenses RDF data extracted by
hcard2rdf.xsl
from the 2006 vCard/RDF work.



The GRDDL aware agent can then use that profileTransformation to extract all hcard data from pages that reference that link.

XML and transformations

In a similar fashion to XHTML, GRDDL transformations can be attached to XML documents.

XML namespace transformations

Just like a profileTransformation, an XML namespace can have a transformation associated with it.
This allows entire XML dialects to provide meaningful RDF.
An XML document simply points to a namespace





and when fetched, points to a namespaceTransformation.
This also allows very large amounts of the existing XML data in the wild to become RDF/XML with minimal effort from the namespace author.

Output

Once a document has been transformed, there is an RDF representation of that data.
This output is generally put into a database and queried via SPARQL.

Implementations

GRDDL consumers (also known as GRDDL aware agents)