Jena

Jena is an open source Semantic Web framework for Java. It provides an API to extract data from and write to RDF graphs. (Wikipedia)

Setup

Setup of Jena with Pellet, which is an open source Java OWL DL reasoner.

Requirements:

• Java 7
• Eclipse IDE

Download and unpack

• Jena (binaries > ZIP file)
• Pellet

Setup Eclipse project

• Create a User Library named Jena > Add External JARs > select all jar files in the Jena lib folder
• Create also a library named Pallet and add all jar from the pallet lib folder (the JARs form the subfolders are not necessary)
• Download Chapter 2 ZIP file which includes a Hello World Eclipse project for semantic web
  • Import the download Eclipse project and add both User Libraries to the Java build path
• Run the file in the src folder

Example

Simple example

import com.hp.hpl.jena.vocabulary.*;
import com.hp.hpl.jena.rdf.model.*;

/*
 * Simple Jena example, which creates a model, adds resources
 * and print the final model on the console. 
 */
public class JenaExample {

	static String namespace = "http://www.example.org/";
	
	public static void main(String ... args) {
		Model m = ModelFactory.createDefaultModel();
		m.setNsPrefix("example", namespace);
		m.setNsPrefix("rdf", RDF.getURI());
		Resource bmw = m.createResource(namespace + "BWM");
		Resource car = m.createResource(namespace + "Car");
		m.add(bwm, RDF.type, car);
		
		m.write(System.out);
		m.write(System.out, "TURTLE");
	}
}

Read, modify and create RDF file

import java.io.FileOutputStream;
import java.util.Map;

import com.hp.hpl.jena.datatypes.xsd.XSDDatatype;
import com.hp.hpl.jena.rdf.model.*;
import com.hp.hpl.jena.sparql.vocabulary.FOAF;
import com.hp.hpl.jena.util.FileManager;
import com.hp.hpl.jena.util.FileUtils;
import com.hp.hpl.jena.vocabulary.RDF;


public class Simpsons {

	public static void main(String ... args) {
		
		/*
		 * Handle arguments
		 */
		if (args.length < 2) {
			System.err.println("Less arguments");
			System.out.println("Example: input.ttl outout.ttl");
			System.exit(0);
		}

		String inputFile = args[0];
		String inputLang = FileUtils.guessLang(inputFile);
		String outputFile = args[1];
		String outputLang = FileUtils.guessLang(outputFile);
		
		/*
		 * Run program
		 */
		try {
			modifyRDFfile(inputFile, inputLang, outputFile, outputLang);
		} catch (Exception e) {
			System.err.println("Error:");
			System.err.println(e.getMessage());
		}
	}
	
	/**
	 * Modify the given file and save changes in output file
	 * 
	 * @param inputFile
	 *            Input file
	 * @param inputLang
	 *            Input RDF language
	 * @param outputFile
	 *            Output file
	 * @param outputLang
	 *            Output RDF language
	 * @throws Exception
	 */
	private static void modifyRDFfile(String inputFile, String inputLang, String outputFile, String outputLang) throws Exception {
		/*
		 * Create model from file
		 */
		Model model = FileManager.get().loadModel(inputFile, inputLang);
		
		/*
		 * Get prefixes
		 */
		@SuppressWarnings("unchecked")
		Map<String, String> prefixMap = model.getNsPrefixMap();

		String sim = prefixMap.get("sim"); 
		String fam = prefixMap.get("fam");
		
		/*
		 * Get properties
		 */
		Property foafAge = model.getProperty(FOAF.NS + "age");
		Property famHasSpouse = model.getProperty(fam + "hasSpouse");

		/*
		 * Modify resources
		 */		
		// Mona
		Resource simMona = model.getResource(sim + "Mona");
		simMona.addProperty(RDF.type, FOAF.Person);
		simMona.addProperty(FOAF.name, "Mona Simpson");
		simMona.addProperty(foafAge, "70", XSDDatatype.XSDint);
		// Abraham
		Resource simAbraham = model.getResource(sim + "Abraham");
		simAbraham.addProperty(RDF.type, FOAF.Person);
		simAbraham.addProperty(FOAF.name, "Abraham Simpson");
		simAbraham.addProperty(foafAge, "78", XSDDatatype.XSDint);
		// Abraham is the spouse of Mona, and Mona is the spouse of Abraham
		model.add(simAbraham, famHasSpouse, simMona);
		model.add(simMona, famHasSpouse, simAbraham);
		
		/*
		 * Iterate about all resource of type foaf:Person  
		 */
		ResIterator foafPersonIterator = model.listResourcesWithProperty(RDF.type, FOAF.Person);
		Resource foafPerson;
		while (foafPersonIterator.hasNext()) {
			foafPerson = foafPersonIterator.nextResource();
			if (foafPerson.hasProperty(foafAge)) {
				int age = foafPerson.getProperty(foafAge).getInt();
				if(age < 18) {
					foafPerson.addProperty(RDF.type, model.getResource(fam + "Minor"));					
				}
				if(age > 70){
					foafPerson.addProperty(RDF.type, model.getResource(fam + "Old"));
				}
			}
		}
		
		/*
		 * Write model into file
		 */
		model.write(new FileOutputStream(outputFile), outputLang);		
	}	
}

SPARQL

see Jena - SPARQL

See also

• RDF
• Jena - RDF Schema
• SPARQL

External links

• Official site