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    • VOS.VirtCrawlerSPARQLEndpoints(1.1) -- DAVWikiAdmin? , 2017-06-13 05:49:29 Edit
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    WebDAV System Administrator 2017-06-13 05:49:29

    Setting up a Content Crawler Job to Retrieve Content from SPARQL endpoint

    The following step-by guide walks you through the process of:

    • Populating a Virtuoso Quad Store with data from a 3rd party SPARQL endpoint
    • Generating RDF dumps that are accessible to basic HTTP or WebDAV user agents.

    1. Sample SPARQL query producing a list SPARQL endpoints: 

      PREFIX rdf:      <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs:     <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl:      <http://www.w3.org/2002/07/owl#>
PREFIX xsd:      <http://www.w3.org/2001/XMLSchema#>
PREFIX foaf:     <http://xmlns.com/foaf/0.1/>
PREFIX dcterms:  <http://purl.org/dc/terms/>
PREFIX scovo:    <http://purl.org/NET/scovo#>
PREFIX void:     <http://rdfs.org/ns/void#>
PREFIX akt:      <http://www.aktors.org/ontology/portal#>

SELECT DISTINCT ?endpoint 
WHERE 
  { 
    ?ds a void:Dataset . 
    ?ds void:sparqlEndpoint ?endpoint 
  }

    2. Here is a sample SPARQL protocol URL constructed from one of the sparql endpoints in the result from the query above: 

      http://void.rkbexplorer.com/sparql/?query=PREFIX+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E+%0D%0APREFIX+void%3A+++++%3Chttp%3A%2F%2Frdfs.org%2Fns%2Fvoid%23%3E++%0D%0ASELECT+distinct+%3Furl++WHERE+%7B+%3Fds+a+void%3ADataset+%3B+foaf%3Ahomepage+%3Furl+%7D%0D%0A&format=sparql

    3. Here is the cURL output showing a Virtuoso SPARQL URL that executes against a 3rd party SPARQL Endpoint URL: 

      $ curl "http://void.rkbexplorer.com/sparql/?query=PREFIX+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E+%0D%0APREFIX+void
%3A+++++%3Chttp%3A%2F%2Frdfs.org%2Fns%2Fvoid%23%3E++%0D%0ASELECT+distinct+%3Furl++WHERE+%7B+%3Fds+a+void%3ADataset+%3B+foaf%3Ah
omepage+%3Furl+%7D%0D%0A&format=sparql"
<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
  <head>
    <variable name="url"/>
  </head>
  <results ordered="false" distinct="true">
    <result>
      <binding name="url"><uri>http://kisti.rkbexplorer.com/</uri></binding>
    </result>
    <result>
      <binding name="url"><uri>http://epsrc.rkbexplorer.com/</uri></binding>
    </result>
    <result>
      <binding name="url"><uri>http://test2.rkbexplorer.com/</uri></binding>
    </result>
    <result>
      <binding name="url"><uri>http://test.rkbexplorer.com/</uri></binding>
    </result>
    ...
    ...
    ...
  </results>
</sparql>

    4. Go to Conductor UI. For ex. http://localhost:8890/conductor :



    5. Enter dba credentials
    6. Go to "Web Application Server"-> "Content Management" -> "Content Imports"



    7. Click "New Target"



    8. In the presented form enter for ex.:
      • "Crawl Job Name": voiD store
      • "Data Source Address (URL)": the url from above i.e.: 

        http://void.rkbexplorer.com/sparql/?query=PREFIX+foaf%3A+%3Chttp%3A%2F%2Fxmlns.com%2Ffoaf%2F0.1%2F%3E+%0D%0APREFIX+void%3A+++++%3Chttp%3A%2F%2Frdfs.org%2Fns%2Fvoid%23%3E++%0D%0ASELECT+distinct+%3Furl++WHERE+%7B+%3Fds+a+void%3ADataset+%3B+foaf%3Ahomepage+%3Furl+%7D%0D%0A&format=sparql

      • "Local WebDAV Identifier": 

        /DAV/void.rkbexplorer.com/content

      • "Follow links matching (delimited with ;)": 

        %

      • Un-hatch "Use robots.txt" ;
      • "XPath expression for links extraction": 

        //binding[@name="url"]/uri/text()

      • Hatch "Semantic Web Crawling";
      • "If Graph IRI is unassigned use this Data Source URL:": enter for ex: 

        http://void.collection

      • Hatch "Follow URLs outside of the target host";
      • Hatch "Run "Sponger" and "Accept RDF"




    9. Click "Create".
    10. The target should be created and presented in the list of available targets:



    11. Click "Import Queues":



    12. Click "Run" for the imported target:



    13. To check the retrieved content go to "Web Application Server"-> "Content Management" -> "Content Imports" -> "Retrieved Sites":



    14. Click voiD store -> "Edit":



    15. To check the imported URLs go to "Web Application Server"-> "Content Management" -> "Repository" path DAV/void.rkbexplorer.com/content:



    16. To check the inserted into the RDF QUAD data go to http://cname/sparql and execute the following query: 

      SELECT * 
FROM <http://void.collection> 
WHERE 
  {
    ?s ?p ?o
  }









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