xfolk-to-rdf-old
xFolk → RDF
by Toby Inkster
This article describes a method for converting an xFolk object into RDF triples and suggests ways of using RDFa or eRDF to extend xFolk, adding additional information about the xFolk object, and about the article that has been linked to.
Digg is an example of the type of site that could make use of xFolk, but in April 2008 they instead implemented support for RDFa. Their choice of RDF for representing tagged links is used as the basis for this article.
The Triples
The Subject
RDF represents all information in the form of "triples". The first part of a triple is the subject - a URI for the thing being described. Although at first the obvious choice for the subject might be the URI of the tagged link (and this is how I initially implemented xFolk→RDF), Digg instead uses its own page as the subject. So for our triple, the subject will be the URI of the xFolk object itself. The URI can be determined like this:
- If the tag with
class="xfolkentry"is a<body>element, then the subject URI is the URI of the page being parsed. - Otherwise, if the tag with
class="xfolkentry"has anidattribute, then the subject URI is the page URI followed by a hash symbol (#) followed by the contents of theidattribute. - Lastly, if none of the above applies, then there is no subject URI, so a BNode is created.
The Predicates
The following predicates are used:
- http://purl.org/dc/terms/title or http://purl.org/dc/elements/1.1/title
- http://purl.org/dc/terms/source or http://purl.org/dc/elements/1.1/source
- http://purl.org/dc/terms/abstract
(Editor's note: I've not 100% decided the best way of representing tags. Will get there soon though.)
The Objects
The object of dcterms:source is a resource with the URI found in the href attribute of the element with class="taggedlink".
The object of dcterms:title is a string literal consisting of the contents of the element with class="taggedlink".
The object of dcterms:abstract is a string literal consisting of the contents of the element with class="description".
An Example
The following example xFolk entry is included in the xFolk specification (ID attribute added for the purposes of illustration):
<div class="xfolkentry" id="rtags">
<div>
<a class="taggedlink" href="http://www.sifry.com/alerts/archives/000306.html">
Sifry's Alerts: Technorati launches Related Tags
</a>
</div>
<div class="description">
Ever wanted to see what posts are related to other posts, what tags
are related to others? Now you can! Just check under the Tag
description on most tag pages, like this one, or this one, and you'll
see the patterns. Can you smell the emergence?
</div>
<div class="meta">
to
<a rel="tag" href="/fpgibson/folksonomy">folksonomy</a>
<a rel="tag" href="/fpgibson/technorati">technorati</a>
... <a class="delNav" href="/url/cbcabf7de070fdb46598ee679367be49">
and 1 other person
</a>
... on 2005-04-09
</div>
</div>
The above could generate the following RDF/XML:
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/dc/terms/">
<rdf:Description rdf:about="http://example.org/#rtags">
<dc:source rdf:resource="http://www.sifry.com/alerts/archives/000306.html" />
<dc:title>Sifry's Alerts: Technorati launches Related Tags</dc:title>
<dc:abstract>
Ever wanted to see what posts are related to other posts, what tags
are related to others? Now you can! Just check under the Tag
description on most tag pages, like this one, or this one, and you'll
see the patterns. Can you smell the emergence?
</dc:abstract>
</rdf:Description>
</rdf:RDF>
Extending xFolk with RDFa
Because the xFolk entry and the link each have a URI, they can be used as subjects in RDFa:
<dl>
<dt>Page by</dt>
<dd about="http://www.sifry.com/alerts/archives/000306.html"
property="dc:creator">Sifry</dd>
<dt>Page published on</dt>
<dd about="http://www.sifry.com/alerts/archives/000306.html"
property="dc:date">2005-04-09</dd>
<dt>Link submitted by</dt>
<dd about="#rtags" property="dc:creator">Alice Jones</dd>
<dt>Link submitted on</dt>
<dd about="#rtags" property="dc:date">2005-04-11</dd>
</dl>
Added to the earlier HTML example, this ends up as:
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/dc/terms/">
<rdf:Description rdf:about="http://example.org/#rtags">
<dc:source>
<rdf:Description rdf:about="http://www.sifry.com/alerts/archives/000306.html">
<dc:creator>Sifry</dc:creator>
<dc:date>2005-04-09</dc:date>
</rdf:Description>
</dc:source>
<dc:title>Sifry's Alerts: Technorati launches Related Tags</dc:title>
<dc:abstract>
Ever wanted to see what posts are related to other posts, what tags
are related to others? Now you can! Just check under the Tag
description on most tag pages, like this one, or this one, and you'll
see the patterns. Can you smell the emergence?
</dc:abstract>
<dc:creator>Alice Jones</dc:creator>
<dc:date>2005-04-11</dc:date>
</rdf:Description>
</rdf:RDF>
Extending xFolk with eRDF
eRDF can be used instead of RDFa, however due to limitations of eRDF syntax, it can only be used to specify additional metadata about the xFolk entry, and not the tagged link.
Related Pages
xFolk
Microformats to RDF
See also: