Hello Heiner,
this option seems to work:
CONSTRUCT {
?this base:_result ?result .
}
WHERE {
{
SELECT ((SUM(?value)) AS ?result) ?this
WHERE {
?this base:has/base:_property ?value .
}
GROUP BY ?this
} .
}
Note the GROUP BY.
But in general, as you state, SPARQL is executed from the inside out and
pre-bound variables may not be visible in sub-selects. I usually avoid
such cases by turning the sub-select into a SPIN function. The query
would then be something like
CONSTRUCT {
?this base:_result ?result .
}
WHERE {
BIND (ex:computeResult(?this) AS ?result) .
}
and the spin:body of ex:computeResult would be
SELECT ((SUM(?value)) AS ?result)
WHERE {
?arg1 base:has/base:_property ?value .
}
HTH
Holger
On 5/24/2013 23:26, Heiner Reinhardt wrote:
Hello,
I am trying to create a spin rule that allows for the aggregation of
values.
Let's think of a simple basis ontology (
a1 has b1 .
a1 has b2 .
a2 has b1 .
b1 _property 5 .
b2 _property 2 .
a1 rdf:type A .
a2 rdf:type B .
I would like to create the triples saying:
a1 _result 7 .
a2 _result 5 .
which then provide the result of (5+2) and (5) (aggregation as a SUM)
I tried to work with two different queries:
Query A
CONSTRUCT {
?this base:_result ?result
}
WHERE {
{
SELECT ( SUM( ?value ) AS ?result )
WHERE { ?this rdf:type base:A . ?this base:has ?b . ?b
base:_property ?value }
}
}
It seems that it does not get executed at all.
Query B
CONSTRUCT {
?this base:_result ?result
}
WHERE {
?this rdf:type base:A
{
SELECT ( SUM( ?value ) AS ?result )
WHERE { ?this rdf:type base:A . ?this base:has ?b . ?b
base:_property ?value }
}
}
This query seems to get executed, but ?result is bound to 12 instead
of 7 or 5. It seems that ?this within the SUB-SELECT is not bound to
the respective instance in the SUB-Query.
The w3c specification for SPARQL-subqueries says that bound variables
should not be forwarded to sub queries in order to allow for parallel
execution of the queries.
What is the specification for SPIN?
How would I aggregate some values with SPIN and create a new triple
with this aggregated value based on a specific "?this" ?
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