The formal description is the helper operation 'Substitute'
http://www.w3.org/TR/sparql11-query/#defn_substitute
and the evaluation text just below that. SERVICE isn't special in
anyway (whether it should be is whole different question!).
Andy
On 23/12/14 19:50, Daniel Hernández wrote:
The motivation of my question was to confirm that occurrences of ?x must
be replaced by bindings in each of the solutions before sending the
query to another service. But I do not found a simpler way to write that
question. That's all.
Thanks!
Daniel
On Tue, 2014-12-23 at 18:49 +0000, Andy Seaborne wrote:
>> What will be the result of this query?
Empty.
Firstly - the <a> in the query is highly unlikely to be the same <a> as
the data because the query and data have different base URIs. thsi
appies to the SERVICE and non-SERVICE cases.
The URI resolution of the query is at parse time so <p> inside the
SERVICE is the same <p> in the triple pattern
Adding a stable BASE, I get no results with Fuseki2 because the EXISTS
?x is substituted from the pattern.
The Fuseki2 log shows a call back of:
Query = SELECT * WHERE { <http://example/b> <http://example/p>
<http://example/c>}
which I guess is the core of your question?
Andy
----------------------------
BASE <http://example/>
<a> <p> <b> .
<a> <q> <c> .
----------------------------
BASE <http://example/>
SELECT *
WHERE {
{ <a> <p> ?x }
FILTER (
EXISTS { SERVICE <http://localhost:3030/ds/query> { ?x <p> <c> } }
)
}
----------------------------
On 23/12/14 15:04, Miguel Bento Alves wrote:
Daniel,
what is the point?
You didn’t clear if you have also a local dataset, but I think that the answer
is the same, the result is empty. Why should be different?
(in this situations, normally, I test. Seeing is believing :) ).
In your dataset, instead of <a> <q> <c> you mean <a> <p> <c>?
Miguel
On 23 Dec 2014, at 14:34, Daniel Hernández <[email protected]> wrote:
Hello,
Let us consider a service <s> which default dataset contains the default
graph:
<a> <p> <b> .
<a> <q> <c> .
Let us consider the following query to be evaluated with the service <s>
described above:
SELECT *
WHERE { { <a> <p> ?x } FILTER ( EXISTS ( ?x <p> <c> ) ) }
I suppose that in this case the filter clause is evaluated for each
solution of the graph pattern on the left. Thus, it is evaluated for
{?x:<b>} and {?x:<c>}. Then the clauses will be:
{?x:<b>} --> EXISTS ( <b> <p> <c> ) (FALSE)
{?x:<c>} --> EXISTS ( <c> <p> <c> ) (FALSE)
Then, the result of this query will be empty.
Let us to consider the following query:
SELECT *
WHERE { { <a> <p> ?x }
FILTER ( EXISTS ( SERVICE <s> { ?x <p> <c> } ) ) }
What will be the result of this query?
Regards,
Daniel
