Binary Relations

The default syndication output from WordPress is okay, but does leave room for improvement - even though it “defaults” to RSS 2.0, there’s RSS 1.0 hidden behind the scenes.

The first order of action is to fix the default page template to point to the RDF/XML output instead of RSS 2.0. In the file /index.php there are link elements in the head section of the HTML output, switching to RSS 1.0 is quite easy, simply change the RSS 2.0 line to the following (and remove the link to the 0.92 version):

<link rel="alternate" type="application/rdf+xml" title="RSS 1.0" href="<?php bloginfo('rdf_url'); ?>" />

In the meta section there is also a couple of links, one for RSS 2.0 that will be replaced by a link to RSS 1.0, and one for comments that is just dropped (an RDF/XML version may be added at a later date):

<li><a href="<?php bloginfo('rdf_url'); ?>" title="<?php _e('Syndicate this site using RSS'); ?>"><?php _e('<abbr title="RDF Site Summary">RSS</abbr> 1.0'); ?></a></li>

Now to the actual content of the RSS file: The default template includes, for each post, a dc:creator property that looks like this:

<dc:creator>mortenf (mailto:mort&#101;n&#64;&#119;as&#97;b.dk)</dc:creator>

That’s not terribly helpful for the Semantic Web, so I’ve hacked the template wp-rdf.php to include the following FOAF structure instead:

<foaf:maker>
  <foaf:Person>
    <foaf:name><?php the_author_firstname(); print ' '; the_author_lastname() ?></foaf:name>
    <foaf:nick><?php the_author_login() ?></foaf:nick>
    <foaf:mbox_sha1sum><?php print(bin2hex(mhash(MHASH_SHA1,'mailto:'.$authordata->user_email))) ?></foaf:mbox_sha1sum>
    <foaf:weblog rdf:resource="<?php bloginfo_rss('url') ?>"/>
  </foaf:Person>
</foaf:maker>

In addition to this improvement, the indication of categories could also use a little tune-up. The default output shows categories through the use of dc:subject, which is quite allright but somewhat too vague - how could anyone know that my category SemWeb/FOAF is essentially the same as Danny Ayers‘ Knowledge/FOAF category? To make up for this, it is possible to use the Description field in WordPress’ category system to assign a URI to each (or some) of the categories, and then generate appropriate statements by adding two lines to the the_category_rss template function in /wp-includes/template-functions-category.php:

if(preg_match('|^w+:.+/|',$category->category_description))
    $the_list .= '<foaf:topic rdf:parseType="Resource"><dc:title>'.$category->cat_name.'</dc:title><foaf:page rdf:resource="'.$category->category_description.'"/></foaf:topic>';

The results of these tweakings should show up nicely in the RSS feed - check it out here.