RDF : Resource Description Framework

The basis of the Semantic Web

Jean-François Perrot

  1. Tools

  2. RDF
    1. Introduction, from the Jena Tutorial
    2. Tools
    3. More on RDF's XML Syntax, from the RDF Primer
    4. Extracting RDF contents from standard XML documents
    5. A special syntax for rdf:type

  3. SPARQL
    1. A query language for RDF.
    2. Execution
    3. SPARQL by example : SELECT
    4. SPARQL by example : CONSTRUCT

  4. RDFa & DBPedia
    1. RDFa : mixing XHTML & RDF
    2. Querying DBPedia
    3. Doing it with PHP

  1. Tools


  2. RDF


  3. SPARQL


  4. RDFa & DBPedia

    1. RDFa : mixing XHTML & RDF

    2. Querying DBPedia

      via its SPARQL endpoint : http://dbpedia.org/sparql

      [How to proceed]

      Asking for Mary Shelley's birthdate :
      select ?bd where {
        <http://dbpedia.org/resource/Mary_Shelley> <http://dbpedia.org/ontology/birthDate> ?bd
      }

      for her birthplace
      select ?bp where {
        <http://dbpedia.org/resource/Mary_Shelley> <http://dbpedia.org/ontology/birthPlace> ?bp
      }

      for the country where she was born
      PREFIX dbpedia: <http://dbpedia.org/resource/>
      PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>
      select ?bc where {
               dbpedia:Mary_Shelley dbpedia-owl:birthPlace ?bp .
               ?bp dbpedia-owl:country ?bc
      }

    3. Doing it with PHP

      Composing a HTTP Get query from SPARQL
      function makeHTTPQuery($term){
          $format = 'xml';
          $query =
          "PREFIX dbp: <http://dbpedia.org/resource/> ont : <http://dbpedia.org/ontology/>
           SELECT ?bd
           WHERE {
               dbp:$Mary_Shelly ont:birthDate> ?bd
           }";
         
          $endpoint =       'http://dbpedia.org/sparql';
                $searchUrl = $endpoint.'?'.'query='.urlencode($query).'&format='.$format;
          return $searchUrl;
      }//makeHTTPQuery

      Sending a HTTP Get query with cURL, response as an XML string :
      function sendQuery($searchUrl){
          // get curl handle
          $ch = curl_init();
          // set request url
          curl_setopt($ch, CURLOPT_URL, $searchUrl);
          // set option "return response", don't print/echo
          curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
          // get the response
          $response = curl_exec($ch);
          curl_close($ch);
          return $response;
      }//sendQuery

      Extract info from XML string
      function extractDate ($xmlString){
          $splDoc = new SimpleXMLElement($xmlString);
          $splDoc->registerXPathNamespace('s', 'http://www.w3.org/2005/sparql-results#');
          $pathb = "/s:sparql/s:results/s:result/s:binding[@name='bd']/s:literal/text()";
          $bds = $splDoc->xpath($pathb); // array
          return $bds[0];
      }//extractDate

      Let us add a function to display the date in a format more civil than xsd:date : decoDate.php
      in order to make it clear that obtaining the date of birth is only one step in a process which may be quite elaborate.

      Complete script : birthDate.php