Getting Started With Ontotext GraphDB and RDF4J

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In this post, I will explain how to quickly get started with the free version of Ontotext GraphDB and RDF4J. Ontotext GraphDB is an RDF datastore and RDF4J is a Java framework for accessing RDF datastores (not just GraphDB). I will explain:

  1. how to install and start GraphDB, as well as how to use the workbench to add a repository.
  2. how to do SPARQL queries against GraphDB using RDF4J.

Install and Start GraphDB and Create a Repository

To gain access to the free version of GraphDB you have to email Ontotext. They will respond with an email with links to a desktop and stand-alone server version of GraphDB. You want to download the stand-alone server version. This is a graphdb-free-VERSION-dist.zip file, that you can extract somewhere on your filesystem, which I will refer to here as $GRAPHDB_ROOT. To start GraphDB, go to $GRAPHDB_ROOT/bin and run ./graphdb.

To access the workbench you can go to http://localhost:7200. To create a new repository, in the left-hand side menu navigate to Setup>Repositories. Click the Create new repository button. For our simple example, we will use PersonData as a Repository ID. The rest of the settings we leave as-is. At the bottom of the page, you can press the Create button.

Accessing a GraphDB Repository Using RDF4J

To access our PersonData repository we will use RDF4J. Since GraphDB is based on the RDF4J libraries, we only need to include the GraphDB dependencies since these already include RDF4J. Thus, in our pom.xml file we only need to add the following:

 <dependency>
   <groupId>com.ontotext.graphdb</groupId>
   <artifactId>graphdb-free-runtime</artifactId>
   <version>8.5.0</version>
 </dependency>

In our example Java code, we first insert some RDF data and then do a query based on the added data. For inserting data we start a transaction and commit it, or, if it fails we do a rollback. For querying the data we iterate through the TupleQueryResult, retrieving values for the binding variables we are interested in (i.e. name in this case). In line with the TupleQueryResult documentation, we close the TupleQueryResult once we are done.

package org.graphdb.rdf4j.tutorial;
package org.graphdb.rdf4j.tutorial;

import org.eclipse.rdf4j.model.impl.SimpleLiteral;
import org.eclipse.rdf4j.query.BindingSet;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.query.QueryLanguage;
import org.eclipse.rdf4j.query.TupleQuery;
import org.eclipse.rdf4j.query.TupleQueryResult;
import org.eclipse.rdf4j.query.Update;
import org.eclipse.rdf4j.repository.Repository;
import org.eclipse.rdf4j.repository.RepositoryConnection;
import org.eclipse.rdf4j.repository.http.HTTPRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
import org.slf4j.MarkerFactory;

public class SimpleInsertQueryExample {
  private static Logger logger = 
    LoggerFactory.getLogger(SimpleInsertQueryExample.class);
  // Why This Failure marker
  private static final Marker WTF_MARKER = 
    MarkerFactory.getMarker("WTF");

  // GraphDB 
  private static final String GRAPHDB_SERVER = 
    "http://localhost:7200/";
  private static final String REPOSITORY_ID = "PersonData";

  private static String strInsert;
  private static String strQuery;

  static {
    strInsert = 
        "INSERT DATA {"
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://dbpedia.org/ontology/birthDate> \"1906-12-09\"^^<http://www.w3.org/2001/XMLSchema#date> ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://dbpedia.org/ontology/birthPlace> <http://dbpedia.org/resource/New_York_City> ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://dbpedia.org/ontology/deathDate> \"1992-01-01\"^^<http://www.w3.org/2001/XMLSchema#date> ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://dbpedia.org/ontology/deathPlace> <http://dbpedia.org/resource/Arlington_County,_Virginia> ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://purl.org/dc/terms/description> \"American computer scientist and United States Navy officer.\" ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Person> ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://xmlns.com/foaf/0.1/gender> \"female\" ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://xmlns.com/foaf/0.1/givenName> \"Grace\" ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://xmlns.com/foaf/0.1/name> \"Grace Hopper\" ."
         + "<http://dbpedia.org/resource/Grace_Hopper> <http://xmlns.com/foaf/0.1/surname> \"Hopper\" ."        
         + "}";

    strQuery = 
        "SELECT ?name FROM DEFAULT WHERE {" +
        "?s <http://xmlns.com/foaf/0.1/name> ?name .}";
  }  

  private static RepositoryConnection getRepositoryConnection() {
    Repository repository = new HTTPRepository(
      GRAPHDB_SERVER, REPOSITORY_ID);
    repository.initialize();
    RepositoryConnection repositoryConnection = 
      repository.getConnection();
    return repositoryConnection;
  }

  private static void insert(
    RepositoryConnection repositoryConnection) {

    repositoryConnection.begin();    
    Update updateOperation = repositoryConnection
      .prepareUpdate(QueryLanguage.SPARQL, strInsert);
    updateOperation.execute();

    try {
      repositoryConnection.commit();
    } catch (Exception e) {
      if (repositoryConnection.isActive())
        repositoryConnection.rollback();
    }
  }

  private static void query(
    RepositoryConnection repositoryConnection) {

    TupleQuery tupleQuery = repositoryConnection
      .prepareTupleQuery(QueryLanguage.SPARQL, strQuery);
    TupleQueryResult result = null;
    try {
      result = tupleQuery.evaluate();
      while (result.hasNext()) {
        BindingSet bindingSet = result.next();

        SimpleLiteral name = 
          (SimpleLiteral)bindingSet.getValue("name");
        logger.trace("name = " + name.stringValue());
      }
    }
    catch (QueryEvaluationException qee) {
      logger.error(WTF_MARKER, 
        qee.getStackTrace().toString(), qee);
    } finally {
      result.close();
    }    
  }  

  public static void main(String[] args) {
    RepositoryConnection repositoryConnection = null;
    try {   
      repositoryConnection = getRepositoryConnection();

      insert(repositoryConnection);
      query(repositoryConnection);      

    } catch (Throwable t) {
      logger.error(WTF_MARKER, t.getMessage(), t);
    } finally {
      repositoryConnection.close();
    }
  }  
}

Conclusion

In this brief post, I gave a quick example of how you can setup a simple GraphDB repository and query it using SPARQL. You can find sample code on GitHub.

 

 

 

 

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