inkdroid

If you’ve already caught the micro-blogging bug identi.ca is an interesting twitter clone for a variety of reasons…not the least of which is that it’s an open source project, and has been designed to run in a decentralized way. The thing I was pleasantly surprised to see was FOAF exports like this for user networks, and HTTP URIs for foaf:Person resources:

ed@hammer:~$ curl -I http://identi.ca/user/6104
HTTP/1.1 302 Found
Date: Fri, 11 Jul 2008 12:58:56 GMT
Server: Apache/2.2.8 (Ubuntu) PHP/5.2.4-2ubuntu5.1 with Suhosin-Patch
X-Powered-By: PHP/5.2.4-2ubuntu5.1
Status: 303 See Other
Location: http://identi.ca/edsu
Content-Type: text/html

It looks like there’s a slight bug in the way the HTTP status is being returned, but clearly the intent was to do the right thing by httpRange-14. If I have time I’ll get laconi.ca running locally so I can confirm the bug, and attempt a fix.

It’s also cool to see that Evan Prodromou (the lead developer, and creator of identi.ca and laconi.ca) has opened a couple tickets for adding RDFa to various pages. If I have the time this would be a fun hack as well. I’d also like to take a stab at doing conneg at foaf:Person URIs to enable this sorta thing:

ed@hammer:~$ curl -I --header "Content-type: application/rdf+xml" http://identi.ca/user/6104
HTTP/1.1 303 See Other
Date: Fri, 11 Jul 2008 13:08:42 GMT
Server: Apache/2.2.8 (Ubuntu) PHP/5.2.4-2ubuntu5.1 with Suhosin-Patch
X-Powered-By: PHP/5.2.4-2ubuntu5.1
Location: http://identi.ca/edsu/foaf

instead of what happens currently:

ed@hammer:~$ curl -I --header "Content-type: application/rdf+xml" http://identi.ca/user/6104
HTTP/1.1 302 Found
Date: Fri, 11 Jul 2008 13:08:42 GMT
Server: Apache/2.2.8 (Ubuntu) PHP/5.2.4-2ubuntu5.1 with Suhosin-Patch
X-Powered-By: PHP/5.2.4-2ubuntu5.1
Status: 303 See Other
Location: http://identi.ca/edsu
Content-Type: text/html

I guess this is also just a complicated way of saying I’m edsu on identi.ca–and that the opportunity to learn more about OAuth and XMPP is a compelling enough reason alone for me to make the switch.

I’ve set up a SPARQL endpoint for lcsh.info at sparql.lcsh.info. If you are new to SPARQL endpoints, they are essentially REST web services that allow you to query a pool of RDF data using a query language that combines features of pattern matching, set logic and the web, and then get back results in a variety of formats. If you are a regular expression and/or SQL junkie, and like data, then SPARQL is definitely worth taking a look at.

If you are new to SPARQL and/or LCSH as SKOS you can try the default query and you’ll get back the first 10 triples in the triple store:

SELECT ?s ?p ?p
WHERE {?s ?p ?o}
LIMIT 10

As a first tweak try increasing the limit to 100. If you are feeling more adventurous perhaps you’d like to look up all the triples for a concept like Buddhism:

PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT ?s ?p ?o
WHERE {
  ?s ?p ?o .
  ?s skos:prefLabel "Buddhism"@en .
}

Or, perhaps you are interested in seeing what narrower terms there are for Buddhism:

PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT ?uri ?label
WHERE {
  <http://lcsh.info/sh85017454#concept> skos:narrower ?uri .
  ?uri skos:prefLabel ?label
}

Or maybe you don’t know the skos:prefLabel (aka authorized heading), so look for all the lcsh headings that start with Independence

PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT ?s ?label
WHERE {
  ?s skos:prefLabel ?label.
  FILTER regex(?label, '^independence', 'i')
}

Feel free to use the service however you want. I’m interested in seeing what its limitations are.

Benjamin Nowack’s ARC made it extremely easy to load up the 2,441,494 LCSH triples in a few hours with a script like:

include_once('arc/ARC2.php');
 
$config = array(
    'db_name'               => 'arc',
    'db_user'               => 'arc',
    'db_pwd'                => 'notapassword',
    'store_name'            => 'lcsh',
    'store_log_inserts'     => 1,
);
 
$store = ARC2::getStore($config);
 
if (!$store->isSetup()) {
    $store->setUp();
}
 
$store->reset();
$rs = $store->query('LOAD <http://lcsh.info/static/lcsh.nt>');
 
print_r($rs);

Then it’s just a simple matter of putting up a php script like:

/* ARC2 static class inclusion */
include_once('arc/ARC2.php');
 
/* MySQL and endpoint configuration */
$config = array(
  /* db */
  'db_host' => 'localhost', /* optional, default is localhost */
  'db_name' => 'arc',
  'db_user' => 'arc',
  'db_pwd' => 'fakepassword',
 
  /* store name */
  'store_name' => 'lcsh',
 
 
  /* endpoint */
  'endpoint_features' => array(
    'select', 'construct', 'ask', 'describe'
  ),
  'endpoint_timeout' => 60, /* not implemented in ARC2 preview */
  'endpoint_read_key' => '', /* optional */
  'endpoint_write_key' => 'fakekey', /* optional */
  'endpoint_max_limit' => 1000, /* optional */
);
 
/* instantiation */
$ep = ARC2::getStoreEndpoint($config);
 
/* request handling */
$ep->go();

Ideally I would’ve been able to quickly bring up a SPARQL endpoint on top of the rdflib Sleepycat triple store that is being used to serve up the linked data at lcsh.info. But rather that pursuing elegance (this is kinda side work after all), I wanted to quickly put the SPARQL service out there for experimentation, and this was the quickest way for me to do that. If the service proves useful I’ll look more at what it takes to create an rdflib SPARQL service, or porting over the little python code I have to php (gasp).