On 7/23/14 6:43 AM, james anderson wrote:
good afternoon;On 11 Jul 2014, at 10:38, Carsten Keßler<m...@carsten.io> wrote:>Dear all, > >I'm running Virtuoso OS 7.1.0 and trying to run some federated queries to DBpedia and Europeana. Here's an example of what I'm trying to do (fetch some Europeana artifacts created during the lifetime of Ghandi, as a simplified example): > >prefix db:<http://dbpedia.org/ontology/> >prefix dc:<http://purl.org/dc/elements/1.1/> >prefix xsd:<http://www.w3.org/2001/XMLSchema#> > >SELECT * WHERE { > > SERVICE<http://dbpedia.org/sparql> { > <http://dbpedia.org/resource/Mahatma_Gandhi> db:birthDate ?birth ; > db:deathDate ?death . > > } > > SERVICE<http://europeana.ontotext.com/sparql> { > SELECT * WHERE { > ?artifact dc:date ?date . > FILTER ( ?date >= xsd:string(?birth) && ?date <= xsd:string(?death) ) > } LIMIT 10 > } > >} LIMIT 10 > >If I run this through the sparql.org endpoint, it works without problems [1]. Virtuoso gives me the following error, though: > >Virtuoso 37000 Error SP031: SPARQL compiler: Variable 'birth' is used in the query result set but not assigned >Is this a know limitation of Virtuoso? > >Thanks, >CarstenNotwithstanding the sparql.org response, the description of variable scope[1] provides no binding for either ?birth or ?death, which lends support to virtuoso’s compiler. See, for example, the ‘minus’ example[2]. One might argue that the discussion in the federation spec[3] would lead one to believe that the sparql.org behavior is a reasonable extension. I would agree, but nothing in the federation semantics requires it. best regards, from berlin, ----- [1]http://www.w3.org/TR/sparql11-query/#variableScope [2]http://www.w3.org/TR/sparql11-query/#idp899488 [3|http://www.w3.org/TR/sparql11-federated-query/#values
Thus, you have:[1] http://bit.ly/sparql-fed-query-results-from-virtuoso-uriburner-and-european-sparql-endpoints -- Query Result [2] http://bit.ly/sparql-query-definition-for-sparql-fed-over-uriburner-and-europeana-endpoints -- Query Definition.
The order of SERVICE bindings in the query matters. -- Regards, Kingsley Idehen Founder & CEO OpenLink Software Company Web: http://www.openlinksw.com Personal Weblog 1: http://kidehen.blogspot.com Personal Weblog 2: http://www.openlinksw.com/blog/~kidehen Twitter Profile: https://twitter.com/kidehen Google+ Profile: https://plus.google.com/+KingsleyIdehen/about LinkedIn Profile: http://www.linkedin.com/in/kidehen Personal WebID: http://kingsley.idehen.net/dataspace/person/kidehen#this
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