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I am trying to make a federated query using my local GraphDB database and SPARQL endpoint. For some reason I always get errors or empty columns in my result table.

I tried several SPARQL endpoints which are working perfectly fine on FactForge. My code and error message are below can you help me to get it working.

PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX bif: <bif:>
SELECT ?duration1 ?duration2{ 
    VALUES (?start ?end)
        {("2011-02-02T14:45:14"^^xsd:dateTime "2011-02-04T14:45:13"^^xsd:dateTime)}
    SERVICE <http://dbpedia.org/sparql>           #-- Virtuoso
        { BIND ((?end - ?start)/86400.0 AS ?duration1) }
}

Error 500: error Query evaluation error: org.eclipse.rdf4j.query.QueryEvaluationException: Virtuoso 22023 Error Can not load own service description

I am using the free version of GraphDB. My OS is macOS Mojave 10.14.5. I directly installed GraphDB from the website and i never used RDF4J before. Also after this error i installed a local Virtuoso SPARQL endpoint and i can use federated query from that endpoint using my local GraphDB as a service. But i cannot use federated query from my local GraphDB endpoint using my local Virtuoso endpoint as a service since it gives the same error above.

dogu
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    (1) When testing and asking something like this, it's best to start with a [SIMPLE query that shows the issue](https://stackoverflow.com/help/minimal-reproducible-example), optimally one that can be reproduced entirely on public services. (2) The reported error appears to have come from RDF4J, not GraphDB, and appears to show RDF4J talking directly to the DBpedia instance (Virtuoso), so I'm not sure how you're doing what you're doing... Please try to simplify your test setup, and then describe it in more detail. – TallTed Sep 13 '19 at 14:18
  • Regarding the rdf4j error, this could be caused by GraphDB using parts of rdf4j under the hood. It's not necessarily a consequence of OP doing anything odd in their setup. – Jeen Broekstra Sep 16 '19 at 06:55

1 Answers1

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The root cause of the above error is "Virtuoso 22023 Error Can not load own service description", which is handled as an unknown runtime exception resulting HTTP Code 500.

I suspect this was a temporal glitch in the DBPedia service since the same query currently works from GraphDB tested with the latest GraphDB 9.0 versions and an older GraphDB 8.x version via FactForge service.

vassil_momtchev
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  • I can also do it on FactForge but in my local machine (macOS Mojave 10.14.5) while using the GraphDB Free version i still have the same problem. I used a workaround by installing a Docker image for the Free version and now i can do federated queries. – dogu Nov 06 '19 at 20:19