The specification says "EVERY occurrence":
substitute(pattern, μ) = the pattern formed by replacing every
occurrence of a variable v in pattern by μ(v) for each v in dom(μ)
However, I guest that it must be only occurrences in basic graph
patterns. For example, let us to consider the pattern:
P = VALUES (?x) { ("a") }
What is the result of substitute(P, {?x: "x"})?
If I substitute every occurrence, then I will get:
VALUES ("x") { ("a") }
But the domain of mappings is limited to variables. So I guest that the
result must be:
VALUES (?x) { ("a") }
Lets consider P2 = {:s :p ?x} . VALUES (?x) { ("a") }. Then, I guest
that substitue(P2, {?x: "x"}) must be:
{:s :p "x"} . VALUES (?x) { ("a") }
On Tue, 2014-12-23 at 20:22 +0000, Andy Seaborne wrote:
> 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
> >>>>
> >>>
> >>
> >
> >
>
