Hi Curran, Il 27/05/2011 4.36, Curran Kelleher ha scritto:
According to the SPARQL reference <http://www.w3.org/TR/rdf-sparql-query/#modDistinct>, DISTINCT should even be an operation able to be performed after evaluation of LIMIT which just collapses duplicate entries in the intermediary result set into single entries in the final result set... Am I mistaken with this? Is there something more to the definition of DISTINCT than the requirement that no duplicate entry exists in the /result set/ (not in the entire database)?actually the SPARQL reference says "Note that, per the order of solution sequence modifiers <http://www.w3.org/TR/rdf-sparql-query/#solutionModifiers>, duplicates are eliminated before either limit or offset is applied." So DISTINCT acts before, and then LIMIT is applied. So as you can imagine, distinguing all the values in a query like ?s ?p ?o, before limiting the resultset, is onerous on big graphs. This is logical: imagine that LIMIT was executed before, and then DISTINCT: you could obtain less values than what you specified in the LIMIT clause. Neverthless I don't know if in some situations (as Baran was pointing out) some optimizations could be performed. Well, I think Kingsley is the most authoritative man for such answers. :-)
Thanks for bearing with me here :) Best regards, Curran
Best regards, roberto
On Thu, May 26, 2011 at 7:07 PM, Kingsley Idehen <kide...@openlinksw.com <mailto:kide...@openlinksw.com>> wrote:On 5/26/11 5:35 PM, baran_H wrote: > Without 'distinct' it does work: > select ?property where { > ?s ?property ?o. > } limit 1 > > Why might this be? So you are asserting that for a given data space hosting N named graphs (named collections of triples) : select ?property where { ?s ?property ?o. } limit 1 and select distinct ?property where { ?s ?property ?o. } limit 1 and select ?property from <namedGraphIRI> where { ?s ?property ?o. } limit 1 and select ?property where { graph ?g { ?s ?property ?o. } } limit 1 are equivalent. Again, I say, no re. cost of solution. -- Regards, Kingsley Idehen President& CEO OpenLink Software Web: http://www.openlinksw.com Weblog: http://www.openlinksw.com/blog/~kidehen Twitter/Identi.ca <http://www.openlinksw.com/blog/%7Ekidehen%0ATwitter/Identi.ca>: kidehen ------------------------------------------------------------------------------ vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1 _______________________________________________ Dbpedia-discussion mailing list Dbpedia-discussion@lists.sourceforge.net <mailto:Dbpedia-discussion@lists.sourceforge.net> https://lists.sourceforge.net/lists/listinfo/dbpedia-discussion ------------------------------------------------------------------------------ vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1 _______________________________________________ Dbpedia-discussion mailing list Dbpedia-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dbpedia-discussion
-- Roberto Mirizzi http://sisinflab.poliba.it/mirizzi
------------------------------------------------------------------------------ vRanger cuts backup time in half-while increasing security. With the market-leading solution for virtual backup and recovery, you get blazing-fast, flexible, and affordable data protection. Download your free trial now. http://p.sf.net/sfu/quest-d2dcopy1
_______________________________________________ Dbpedia-discussion mailing list Dbpedia-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dbpedia-discussion
