How to publish org-mode to HTML5+RDFa

Principle
Adding a custom link type
Generating HTML5+RDFa

The goal is to ensure I can author HTML5+RDFa easily in org-mode.

Principle

I'd like to add meta-data in the generated HTML exports of a publishing project, while keeping the syntax as compact as possible.

I'm doing this by identifying a few RDFa constructs that will be used frequently, for which I'll add a predefined custom link type.

The following :

[[rlink:link_to_resource :typeof "foaf:Person" :about "http://www-public.telecom-sudparis.eu/~berger_o/foaf.rdf#me" :rel "foaf:homepage" :href "https://www-public.tem-tsp.eu/~berger_o/"][My homepage]]

will then be exported to HTML as :

<span about="http://www-public.telecom-sudparis.eu/~berger_o/foaf.rdf#me" tyepof="foaf:Person" rel="foaf:homepage"><a href="https://www-public.tem-tsp.eu/~berger_o/">My homepage</a></span>

When Descriptive links is activated, the link will just look like a classical [[https://www-public.tem-tsp.eu/~berger_o/][My homepage]] (i.e. a blue link behind My homepage),which won't clutter the buffer.

I have followed the guidelines set by John Kitchin in Extending the org-mode link syntax with attributes for doing so.

The special rlink link will allow exporting different RDFa constructs :

link_to_resource links like the above,
article resource descriptions for research articles (yeah, my homepage links to my papers ;)

The results can be seen on my My homepage (note that this very link uses the [[rlink: construct : inspect the HTML source of this page :-)..

Adding a custom link type

In this file, we add an emacs-lisp babel code block, that will create a custom link type, named rlink which will allow adding RDFa in our document.

;; Add a new link type to allow embedding RDFa into the exported docs
;; with something like :
;;  [[rlink:link_to_resource :typeof "foaf:Person" :about "http://www-public.telecom-sudparis.eu/~berger_o/foaf.rdf#me" :rel "foaf:homepage" :href "https://www-public.tem-tsp.eu/~berger_o/"]]
;; which will be exported to HTML as :
;;  <span about="http://www-public.telecom-sudparis.eu/~berger_o/foaf.rdf#me" tyepof="foaf:Person" rel="foaf:homepage"><a href="https://www-public.tem-tsp.eu/~berger_o/">https://www-public.tem-tsp.eu/~berger_o/</a></span>
;;

(org-add-link-type
 "rlink"
 ;; RDF link
 ;;  follow function
 nil
 ;; format function
 (lambda (path description backend)
   (cond ((string= backend "html")
          (let* ((data (read (concat "(" path ")")))
                 (head (car data))
                 (plist (cdr data)))
            (cond
             ((string= head "link_to_resource")
              (let ((html "<span")
                     (about (plist-get plist :about))
                     (typeof (plist-get plist :typeof))
                     (rel (plist-get plist :rel))
                     (property (plist-get plist :property))
                     (href (plist-get plist :href)))
                (if about
                    (setq html (concat html (format " about=\"%s\"" about))))
                (if typeof
                    (setq html (concat html (format " typeof=\"%s\"" typeof))))
                (if rel
                    (setq html (concat html (format " rel=\"%s\"" rel))))
                (if property
                    (setq html (concat html (format " property=\"%s\"" property))))
                (setq html (concat html (format "><a href=\"%s\">" href)))
                (if (not description)
                    (setq description href))
                (setq html (concat html description))
                (setq html (concat html "</a></span>"))

                html)
              )
             ((string= head "article")
              (let ((html "<span")
                     (about (plist-get plist :about))
                     (creator (plist-get plist :creator))
                     (sameas (plist-get plist :sameas)))
                (setq html (concat html (format " about=\"%s\" typeof=\"biblio:Reference\">" about)))
                (if creator
                    (setq html (concat html (format "<span rel=\"dcterms:creator\" resource=\"%s\"></span>" creator))))
                (if sameas
                    (setq html (concat html (format "<span rel=\"owl:sameAs\" resource=\"%s\"></span>" sameas))))
                (setq html (concat html (format "<i><span property=\"dcterms:title\">%s</span></i>" description)))
                (setq html (concat html "</span>"))
                html)
              )
             (t (format "[[%s][%s]]" path description))
             )
            )
          ))
   )
 )

My elisp style can probably be improved (suggestions welcome ;).

To embedd this in the index.org of the publishing project, I'm using :

#+NAME: add-rlink-link-type
#+BEGIN_SRC emacs-lisp :results silent :exports results
  (org-add-link-type
   "rlink"
...
#+END _SRC <--- NOTE: this should be #+END_SRC, so fix it if you copy/paste

At the bottom, I'm adding

# Local Variables:
# org-confirm-babel-evaluate: (lambda (lang body) (not (string= lang "emacs-lisp")))
# End:

This ensures that I'm allowing the add-rlink-link-type invocation at every publishing/export once, when loading index.org.

Generating HTML5+RDFa

The documents need to be adapted so that HTML5 is generated, and so that embedded RDFa is valid.

This requires a few bits (please report missing ones), mainly in the org templates.

Adpating the org templates

The HTML_DOCTYPE needs to be set to xhtml5 and the HTML needs to be valid in the templates. Something like :

#+LANG: fr
#+OPTIONS: html-link-use-abs-url:nil html-postamble:auto
#+OPTIONS: html-preamble:t html-scripts:t html-style:nil
#+OPTIONS: html5-fancy:nil tex:t
#+OPTIONS: num:nil
#+HTML_CONTAINER: div
#+HTML_DOCTYPE: xhtml5

Adding prefixes

The content will be enclosed inside a <div> which will add the necessary RDF prefixes

#+HTML:<div prefix="foaf: http://xmlns.com/foaf/0.1/ org: http://www.w3.org/ns/org# biblio: http://purl.org/net/biblio#">

... content ...

#+HTML:</div>

Citing articles