Semweb4j/rdfs/step2

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[edit] Step 2: Defining a point

Another sample application, defining a WGS84_pos point.

See also: WGS84_pos ontology in RDF.

package org.ontoware.semweb4j.lessons.lesson4;

import org.ontoware.aifbcommons.collection.ClosableIterator;
import org.ontoware.rdf2go.RDF2Go;
import org.ontoware.rdf2go.exception.ModelRuntimeException;
import org.ontoware.rdf2go.model.Model;
import org.ontoware.rdf2go.model.Statement;
import org.ontoware.rdf2go.model.Syntax;
import org.ontoware.rdf2go.model.node.URI;
import org.ontoware.rdf2go.model.node.Variable;
import org.ontoware.rdf2go.vocabulary.RDFS; 

class Point {
	
	private static URI WGS84_Point;
	private static URI WGS84_lat;
	private static URI WGS84_long;
	private static URI WGS84_alt;

	private static Model model;
	
	private URI resource;
	
	public static void init(Model newModel) throws ModelRuntimeException {
		model = newModel;
		WGS84_Point = model.createURI("http://www.w3.org/2003/01/geo/wgs84_pos.rdf#Point");
		WGS84_lat = model.createURI("http://www.w3.org/2003/01/geo/wgs84_pos.rdf#lat");
		WGS84_long = model.createURI("http://www.w3.org/2003/01/geo/wgs84_pos.rdf#long");
		WGS84_alt = model.createURI("http://www.w3.org/2003/01/geo/wgs84_pos.rdf#alt");
	}

You should ask yourself why this static init method is used. The reason is that the URIs created by model.createURI are different for each underlying Model implementation / triple store - so it's not possible to have static URIs without any Model these URIs belong to. It's recommeded to use this solution if you have similar situations in your programs.

	public Point(String latitude, String longitude, String altitude) throws ModelRuntimeException {
		resource = model.newRandomUniqueURI();
		model.addStatement(resource, RDFS.Class, WGS84_Point);
		setLatitude(latitude);
		setLongitude(longitude);
		setAltitude(altitude);
	}
	
	/**
	 * @param property
	 * @return a properties value (if there are many, chosen randomly)
	 */
	private String getProperty(URI property) {
			ClosableIterator<? extends Statement> it = model.findStatements(resource, property, Variable.ANY);
			if (it.hasNext()) {
				String result = it.next().getObject().toString();
				it.close();
				return result;
			}
			else return null;
	}

	private void setProperty(URI property, String value) throws ModelRuntimeException {
		try {
			// removing any values found
			model.removeStatements(resource, property, Variable.ANY);
		} catch (ModelRuntimeException e) {
			// ModelException on removeAll or findStatements => no such statements
		} finally {
			// add one property statement
			model.addStatement(resource, property, value);
		}
	}
	

getProperty & setProperty are used to avoid redundant code.

	public String getAltitude() {
		return getProperty(WGS84_alt);
	}

	public void setAltitude(String altitude) throws ModelRuntimeException {
		setProperty(WGS84_alt, altitude);
	}

	public String getLatitude() {
		return getProperty(WGS84_lat);
	}

	public void setLatitude(String latitude) throws ModelRuntimeException {
		setProperty(WGS84_lat, latitude);
	}

	public String getLongitude() {
		return getProperty(WGS84_long);
	}

	public void setLongitude(String longitude) throws ModelRuntimeException {
		setProperty(WGS84_long, longitude);
	}

	public URI getResource() {
		return resource;
	}
	
}

public class Step2 {
	
	public static void main(String[] args) throws Exception {
		/*
		 * See http://www.w3.org/2003/01/geo/
		 *  and http://www.w3.org/2003/01/geo/wgs84_pos.rdf
		 *  
		 * In WGS84_pos, Point is a subclass of SpatialThing which has
		 *   the properties lat,long,alt which stands for
		 *     latitude (in decimal degrees), a String
		 *     longitude (in decimal degrees), a String
		 *     altitude (in decimal meters above the local reference ellipsoid), a String
		 */
		Model model = RDF2Go.getModelFactory().createModel();
		model.open();

		Point.init(model);
		
		@SuppressWarnings("unused")
		Point A = new Point("0","0","0");
		@SuppressWarnings("unused")
		Point B = new Point("1,4","10,1","0");
		
		model.writeTo(System.out, Syntax.Turtle);
	}

}