Actually, since Gerrit wants just the resource with the latest date, a
SPIN function may be a better route to go. The function body would
be:
SELECT ?lastEvent
WHERE {
?lastEvent a events:InteractionEvent .
?lastEvent events:generatedBy ?arg1 .
?lastEvent events:inXSDDateTime ?last .
}
ORDER BY DESC (?last)
LIMIT 1
...where ?arg1 is passed as a parameter. Then the spin:rule would be:
CONSTRUCT {
?this events:hasLastEvent ?lastEvent .
}
WHERE {
BIND (events:getMaxDateRsc(?this) AS ?lastEvent) .
}
-- Scott
On Jan 4, 1:50 pm, Holger Knublauch <[email protected]> wrote:
> Hi Gerrit,
>
> I am pretty sure that the pre-binding mechanism of SPARQL is not defined for
> sub-selects. ?this is bound by the SPIN engine when the surrounding query
> executes, but this isn't propagated into the sub-query by definition. See
>
> http://www.w3.org/TR/sparql11-query/#subqueries
>
> "Note that only variables projected out of the subquery will be visible, or
> in scope to the outer query."
>
> The work-around is to turn the sub-select into a magic property, where you
> pass in ?this as an argument.
>
> HTH
> Holger
>
> On Jan 4, 2012, at 9:03 PM, Gerrit wrote:
>
>
>
>
>
>
>
> > I'm trying to implement a SPIN rule that will find the last event in a
> > set of events:
>
> > CONSTRUCT {
> > ?this events:hasLastEvent ?lastEvent .
> > }
> > WHERE {
> > SELECT ?lastEvent
> > WHERE {
> > ?lastEvent a events:InteractionEvent .
> > ?lastEvent events:generatedBy ?this .
> > ?lastEvent events:inXSDDateTime ?last .
> > }
> > ORDER BY DESC (?last)
> > LIMIT 1
> > }
>
> > It seems that the SELECT sub-query is evaluated once for ?this, and
> > then used for all other instances of ?this, that results in for
> > example
>
> > events:lamp1 events:hasLastEvent events:event1234
> > events:lamp2 events:hasLastEvent events:event1234
>
> > while events:event1234 is not even related to events:lamp2. The reason
> > why I think this is caused by the ?this keyword in the sub-query, is
> > that executing this query in SPARQL View provides the correct result.
>
> > --
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