GRDDLing DeWitt’s Friends
DeWitt Clinton has a great write-up of Creating a HTML “friends” page from a Google Reader subscription list, a bit of hackery which leads to a hCard microformat-enriched friends list. A little tweak to the HTML can make it more machine-friendly, just adding a HTML Meta Data profile URI:
<head profile="http://www.w3.org/2006/03/hcard">
That profile is GRDDL-enabled, so any GRDDL-aware agent can interpret the source document as RDF. This part’s easy to demonstrate, thanks the online W3C GRDDL service. So I’ve put a tweaked version of the HTML online, and here’s DeWitt’s friends page as RDF (in Turtle syntax, rendered a little verbosely).
Having set this up I realised the data wasn’t actually expressing the friend relationship, so went on to put together some SPARQL to sort that out - below. But afterwards I realised that DeWitt’s HTML was actually expressing the relationships using XFN class names, but again without the profile URI to make it machine-friendly. So another tweak:
<head profile="http://www.w3.org/2006/03/hcard http://www.w3.org/2003/g/td/xfn-workalike">
- the corresponding service output (scroll down to see the extra bits). I suppose I should mention that you can have as many space-separate profiles as you like, and the GRDDL-aware agent will interpret them independently, just accumulating all the triples. The second profile URI adds xfn:friend relationships, I think it would have been more useful with foaf:knows as well, but it is only a demo.One of these days the microformats folks might get around to tweaking the official profile appropriately…
The SPARQL I mentioned looks like this:
prefix rdf:
prefix vcard:
prefix foaf:
CONSTRUCT
{
[ a foaf:Person;
foaf:homepage ;
foaf:name "DeWitt Clinton" ;
]
foaf:knows
[ a foaf:Person;
foaf:homepage ?homepage ;
foaf:name ?name ] .
}
WHERE
{
[ a vcard:VCard ;
vcard:url ?homepage ;
vcard:fn ?name ]
}
- when applied to DeWitt’s data (as RDF), this will map it across from the vCard vocabulary - finding the appropriate ?variables by matching the pattern in the WHERE clause, inserting those ?variables into the CONSTRUCT clause to produce some new RDF.
I tried this on the Redland SPARQL demo, and I think it’s producing the RDF I wanted. Unfortunately the serialization is really ugly - lots of bnodes, and it’s hard to check visually. It appears to confuse Tabulator too, and the W3C RDF Validator which is handy for this kind of visualization appears to be down. (Here’s a copy of the RDF/XML). Still, it was only a workaround - with the right profiles in place it’s not needed.
I’m not sure if there’s a microformat way of expressing that the source data was a subscription/reading list. To get the richest RDF out it might be easier to do what DeWitt did, but to a full RDF serialization rather than microformatted HTML (which is effectively a CustomRdfDialect), producing something like Planet RDF’s blogroll.
