Adding wood to the fire:
What happens in the presence of ORDER BY?
Cheers,
Pablo
On May 27, 2011 4:39 AM, "Curran Kelleher" <[email protected]>
wrote:
> 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 <[email protected]
>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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