text: app.factory("Edge", function(  ) {
  	var createGuid = function() {
  	  function s4() {
  		return Math.floor((1 + Math.random()) * 0x10000)
  				   .toString(16)
  				   .substring(1);
  	  }
  	  return function() {
  		return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
  			   s4() + '-' + s4() + s4() + s4();
  	  };
  	};
  	return function(edgeText, id, from, to){
  		var self = this;
  		this.text = edgeText;
  		this.id = id || createGuid();
  		this.source = from;
  		this.target = to;
  		this.incidentVertexes = function(){
  			return [self.source, self.target];
  		};
  		this.oriented= false;
  	}
  });