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On 03/03/14 16:32, David Booth wrote:
On 02/09/2014 05:45 PM, w3.h...@gmail.com wrote:
Relevant docs:
- Working draft of W3C Note:
https://docs.google.com/document/d/1zGQJ9bO_dSc8taINTNHdnjYEzUyYkbjglrcuUPuoITw/edit#heading=h.wyc73yp7c8jz
I notice that section 6.6.1 Core statistics shows this SPARQL query for
counting the number of triples:
SELECT (COUNT(*) AS ?no) { ?s ?p ?o }
However, I believe the SPARQL 1.1 standard allows duplicate triples and
duplicate query solutions by default. If so, to get an accurate count
of the number of triples, the DISTINCT keyword must be used:
SELECT (COUNT(DISTINCT *) AS ?no) { ?s ?p ?o }
I'm copying Andy Seaborne to see if this is correct, since I could not
easily find this information in the SPARQL 1.1 spec when I did a quick
scan. Andy, am I correct about this?
Thanks,
David
Hi,
In the case of { ?s ?p ?o }, the match is against the default graph and
an RDF graph is a set of triples - so there are no duplicates over the
?s, ?p, ?o elements of a row.
Because of the nature of the pattern, COUNT(*) and COUNT(DISTINCT *)
should be the same.
One suggestion looking at:
SELECT (COUNT(DISTINCT ?g ) AS ?no) { GRAPH ?g { ?s ?p ?o}}
which can be written as:
SELECT (COUNT(?g) AS ?no) { GRAPH ?g { } }
because "GRAPH ?g { }" results in all the graph names, one per row, and
the graph names are distinct so there is no need for DISTINCT in the COUNT.
Andy
