update DOAP.java with default prefix

added reccommended prefix for doap, as in [http://prefix.cc/doap](http://prefix.cc/doap)

Author: seralf

core/model/src/main/java/org/eclipse/rdf4j/model/vocabulary/DOAP.java

@@ -16,8 +16,21 @@
  */
 public class DOAP {
 
+	/**
+	 * The recommended prefix for the DOAP namespace: "doap"
+	 */
+	public static final String PREFIX = "doap";
+	
+	/**
+	 * The DOAP namespace: http://usefulinc.com/ns/doap#
+	 */
 	public static final String NAMESPACE = "http://usefulinc.com/ns/doap#";
 
+	/**
+	 * An immutable {@link Namespace} constant that represents the DOAP namespace.
+	 */
+	public static final Namespace NS = new SimpleNamespace(PREFIX, NAMESPACE);
+	
 	/**
 	 * Classes
 	 */