code: public static void listUnificationXrefsPerPathway(Model model)
  	{
  		// This is a visitor for elements in a pathway - direct and indirect
  		Visitor visitor = new Visitor()
  		{
  			public void visit(BioPAXElement domain, Object range, Model model, PropertyEditor editor)
  			{
  				if (range instanceof physicalEntity)
  				{
  					// Do whatever you want with the pe and xref here
  					physicalEntity pe = (physicalEntity) range;
  					ClassFilterSet<xref,unificationXref> unis = new ClassFilterSet<xref,unificationXref>(pe.getXREF(),
  					                                                                           unificationXref.class);
  					for (unificationXref uni : unis)
  					{
  						System.out.println("pe.getNAME() = " + pe.getNAME());
  						System.out.println("uni = " + uni.getID());
  					}
  				}
  			}
  		};
  
  		Traverser traverser = new Traverser(SimpleEditorMap.L2, visitor);
  
  		Set<pathway> pathways = model.getObjects(pathway.class);
  		for (pathway pathway : pathways)
  		{
  			traverser.traverse(pathway, model);
  		}
  	}
docs: Here is a more elegant way of doing the previous method!
  @param model BioPAX object Model