PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/> 
PREFIX dc: <http://purl.org/dc/elements/1.1/> 
PREFIX swc: <http://data.semanticweb.org/ns/swc/ontology#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>

SELECT ?tag (count(distinct ?s) as ?count)
FROM <http://tw.rpi.edu/2009/ldthon/data/ssn2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/iswc.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/iwod09.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/smr2-2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/wop2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/iswc09.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/hlcs09.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/semrus2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/owled.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swasd2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/ursw2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/ldthon.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/om2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/semrus.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swese2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/iwod2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swui2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/ssws2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swpm2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swasw2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/swui09.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/ck2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/livingweb2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/iswc2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/terra2009.rdf>
FROM <http://tw.rpi.edu/2009/ldthon/data/sdow2009.rdf>
FROM <http://data.semanticweb.org/conference/iswc/2009/complete>
FROM <http://twitlogic.fortytwo.net/mashup/twitlogic-full-sameAsClosure.rdf>
WHERE 
{
  ?s dc:relation ?tag .
}
group by ?tag
order by desc(?count)