Hi Kingsley,
> "Specifically, each solution that binds the same variables to the same RDF
> terms as another solution is eliminated from the solution set." This sounds
> like a first encounter would be added to the result set, and any subsequent
> encounters would simply not be added to the result set.
>
> ...and thus those subsequent encounters wouldn't have any effect on the
result set and therefore wouldn't need to be considered, as far as I can
tell. In other words, as you are traversing the triples and a solution is
added to the result set, won't that solution remain in the result set (under
DISTINCT) regardless of whether there are subsequent encounters of it? The
DISTINCT condition (no duplicates) must hold on the result set only, so I'm
not sure what kind of computation which acts over all triples is necessary
for the "Distinct computation". Could you clarify this?
[Yes, but to a the DBMS cost of figuring out that subsequent encounters
> exist != 0.
>
...but why does the DBMS need to know if subsequent encounters exist if
their existence doesn't effect the result set from the query? or does their
existence change the result of the query? if so how?
I saw your subsequent comment on the various queries not being equivalent,
but what does DISTINCT have to do with named graphs? 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)?
Thanks for bearing with me here :)
Best regards,
Curran
On Thu, May 26, 2011 at 7:07 PM, Kingsley Idehen <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: kidehen
>
>
>
>
>
>
>
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