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<div>In my 
<a href="http://dannyayers.com/archives/2006/02/06/grazing/">last
post</a>, I asserted that although I liked the idea of "grazing",
that OPML isn't all it's cracked up to be. I also said :
<blockquote>
 IÃ¢â¬â¢ll set up one
 or two Ã¢â¬ÅReading
 ListsÃ¢â¬? just to demonstrate that
 simple stuff like this can still be done simply, without having
 to dumb down your world entirely.
</blockquote>
Well I haven't done that yet. But I did have a look at the 
<a href="http://eurekaman.com/opod/">OPod</a> app ("an AJAX OPML
and RSS viewer widget") that 
<a href="http://eirepreneur.blogs.com/">James Corbett</a> had
mentioned. It's a really nice little online data browser.
Here's some data, TimBL's 
<a href="http://www.w3.org/People/Berners-Lee/card.rdf">FOAF
file</a>. Can OPod understand it? Well not really, the FOAF file is
RDF data serialised as RDF/XML, whereas OPod is really looking for
OPML XML.
Although OPML is a sow's ear, such is the capability of the web
(and XML) that folks have been able to use it for things quite silk
pursey. The built-in demo for OPod is the 
<a href="http://eirepreneur.blogs.com/eirepreneur/IrelandDirectory.opml">Open
Ireland Directory</a> OPML, and as the demo shows, that's pretty
sweet.
Ok, at this point you're probably thinking, oh, here comes that
directory in RDF. Not this time (the data is in 
<a href="http://dmoz.org/Regional/Europe/Ireland/">DMOZ</a>, so
presumably quasi-RDF/XML should already be available, or you could
GRDDL the HTML, whatever…).
But I am going to repeat myself : there's nowt wrong with
hierarchical views of web data. It's only when you start
shoehorning web (or general real-world) data into a tree data
structure that I reckon you're on the road to suckiness.
So here's TimBL's 
<a href="http://pragmatron.org/live/outline?uri=http://www.w3.org/People/Berners-Lee/card.rdf">FOAF
as OPML</a>. Had to throw a lot of data away, but it's just about
good enough for OPod. (Actually you might be better trying a FOAF
file of your own - there's some caching going on, an old version of
the OPML seems to be loitering).
Prefix your stuff like this: 
<a href="http://pragmatron.org/live/outline?uri=http://www.aaronsw.com/about.xrdf">http://pragmatron.org/live/outline?uri=http://www.aaronsw.com/about.xrdf</a>
My server's slow and flakey, the code's the result of an hour or
so's clunking, but (when it works) it demonstrate that data can be
flattened in this way.
PS. Sounds like it fell over right away. Ah well. I've had a day
of distractions, this one was marginally more productive than the
others. I'd better make a note of how it should work…(bonus
points to anyone that can set this up only using existing online
services).
Although processing RDF/XML with XSLT is most 
<a href="http://www.semanticplanet.com/library/Main/RdfToTriplesStylesheet">assuredly
possible</a>, there are advantages in dealing with the data at a
model (not least because that's the setup I've got on my
server).
So the RDF/XML gets loaded into an in-memory RDF model
(Redland/Python), onto which the following 
<a href="http://www.w3.org/TR/rdf-sparql-query/">SPARQL</a> is
applied:
<pre>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
</pre>
<pre>
SELECT ?predicate ?object ?name WHERE
{
?subject ?predicate ?object .
 OPTIONAL {
 ?person rdf:type foaf:Person .
 ?person rdfs:seeAlso ?object .
 ?person foaf:name ?name .
 }
}
</pre>
This is currently hard-coded into 
<a href="http://pragmatron.org/trac/file/pragmatron/sparqlsphere/outline_demplex.py">outline_demplex.py</a>,
which is half the code specific to this job. The XML results of the
query are passed through 
<a href="http://pragmatron.org/trac/file/pragmatron/xslt/results-to-opml.xsl">results-to-opml.xsl</a>
to give the OPML, that's the other half.
If the OPTIONAL above is met, then a link to the remote FOAF is
constructed using the person's name as the label, with the URI
being prepended with the rdf2opml conversion. Any other
rdfs:seeAlsos get the same link treatment but without the label.
Literals show as text, bnodes too (OPML hasn't a clue). Any other
resources in the object (i.e. as URIs) are also used as links, but
directly. Except for the FOAF case, the text label on the OPML
element is the predicate URI (a uri2qname xsl snippet would be
useful there). Could no doubt build mini-hierarchies with the
SPARQL/XSLT around people, places or whatever in the source data,
though that's getting to the point where you might as well just use
RDF throughout (or even domain-specific XML).
Other caveats : the OPod tool decides that the target files are
OPML by the filename extension 
(*spluttter*), I was able to trick it at one point with
the suffix on URIs of 
<code>&dummy=.opml</code>, but I can't remember which escaping
version worked… I did briefly try this 
<a href="http://public.yabfog.com/opmlBrowser.php">OPML</a>
browser, but I think the query part in the URI confused it. Bit
more escaping/encoding needed.
See also: 
<a href="http://www.w3.org/2005/ajar/About.html">About the
Tabulator</a>[Danny]
</div>