function nodeRel(PKey, parentNode, childNode, relationType) {
	// private vars
	var m_PKey=PKey;
	var m_parentNode=parentNode;
	var m_childNode=childNode;
	var m_displayDom=document.createElement("div");
	var m_pointsContainer=null; // this is required for deletion, to delete all points one after the other didn't work.
	var m_relationType=(relationType==null)?"main":relationType;
	var m_parentX=0;
	var m_parentY=0;
	var m_childX=0;
	var m_childY=0;
	var m_styleClass="defaultPoint";
	var m_contextMenu=null;

	// properties
	function getPKey() { return(m_PKey); }
	function getParentNode() { return(m_parentNode); }
	function setParentNode(nodeObject) { m_parentNode=nodeObject; }
	function getChildNode() { return(m_childNode); }
	function setChildNode(nodeObject) { m_childNode=nodeObject; }
	function getRelationType() { return(m_relationType); }
	function isMain() { return(m_relationType=="main"); }

	if (arguments.length >= 1) {
		return(construct());	
	} else {
		this.fromXML=fromXML;
		return(this);
	}

	function construct() {
		m_displayDom.setAttribute("id","mmNodeRel_" + m_PKey);
		m_displayDom.appendChild(createPointsContainer());
		m_styleClass=(m_relationType=="main")?"defaultPoint":"freePoint";
		
		// exported functions
		m_displayDom.debugOut=debugOut;	
		m_displayDom.getPKey=getPKey;
		m_displayDom.getParentNode=getParentNode;
		m_displayDom.setParentNode=setParentNode;
		m_displayDom.getChildNode=getChildNode;
		m_displayDom.setChildNode=setChildNode;
		m_displayDom.redraw=redraw;
		m_displayDom.erase=erase;
		m_displayDom.show=show;
		m_displayDom.hide=hide;
		m_displayDom.isMain=isMain;

		m_displayDom.toXML=toXML;
		m_displayDom.fromXML=fromXML;

		document.getElementById("nodeRels").appendChild(m_displayDom);

		return(m_displayDom);
	}
	function show(){
		m_displayDom.style.display="block";
	}
	function hide(){
		m_displayDom.style.display="none";
	}
	function createPointsContainer(){
		m_pointsContainer=document.createElement("div");
		m_pointsContainer.setAttribute("id","mmPointsContainer_" + m_PKey);
		m_pointsContainer.onclick=onPointsContainerClick;
	//	m_pointsContainer.oncontextmenu=onPointsContainerRightClick;
		return(m_pointsContainer);
	}
	function onPointsContainerClick(event){
		if (m_contextMenu==null) {
			var menuItems = new Array();
			menuItems[0]=new menuItem(document.createTextNode("Delete Relation"),erase);
			m_contextMenu=new menuControl(menuItems,1);
			m_pointsContainer.appendChild(m_contextMenu);
			document.addSubscriber(m_contextMenu.hide,"clicked");

		} else {
			m_contextMenu.toggleVisible();
		}
		m_contextMenu.style.top=(event.clientY + window.scrollY) + "px";
		m_contextMenu.style.left=(event.clientX + window.scrollX) + "px";
		return(false);
	}
	function debugOut() {
		var output=("\nPKey: _"+ m_PKey + "_\np/c PKeys:_" + m_parentNode.getPKey() + "/"+ m_childNode.getPKey() +"_ (" + m_relationType + ")" );
		return(output);
	}     
	function redraw() {
		var parentEle=getParentNode();
		var childEle=getChildNode();

		var parentX=parentEle.offsetLeft + (parentEle.offsetWidth/2);
		var parentY=parentEle.offsetTop + (parentEle.offsetHeight/2);

		var childX=childEle.offsetLeft + (childEle.offsetWidth/2);
		var childY=childEle.offsetTop + (childEle.offsetHeight/2);

		// performance: only redraw the line if the corrdinates changed. and both nodes are visible
		if ( ((m_parentX!=parentX) || (m_parentY!=parentY) || (m_childX!=childX) || (m_childY!=childY))
			&& (childEle.style.display != "none") && (parentEle.style.display != "none")) {

			eraseLine();
			drawLine(parentX,parentY,childX,childY,m_styleClass,m_pointsContainer);
			m_parentX=parentX;
			m_parentY=parentY;
			m_childX=childX;
			m_childY=childY;
		}
	}
	function eraseLine() {
		m_displayDom.removeChild(m_pointsContainer);
		m_pointsContainer=createPointsContainer();
		m_displayDom.appendChild(m_pointsContainer);
	}
	function erase() {
		if (isMain()) {
			// new rootnode by deleting main relation.
			rootNode[rootNode.length]=getChildNode();
		}		

		getChildNode().deleteNodeRelation(m_displayDom);
		getParentNode().deleteNodeRelation(m_displayDom);

		m_displayDom.parentNode.removeChild(m_displayDom);
	}
        function toXML(){
                var xmlEle=document.createElement('NODEREL');
                xmlEle.setAttribute("pkey",m_PKey);
                xmlEle.setAttribute("parentnodepkey",m_parentNode.getPKey());
                xmlEle.setAttribute("childnodepkey",m_childNode.getPKey());
                xmlEle.setAttribute("relationtype",m_relationType);
		// including child nodes if this is the main relation
		if (isMain()) { 
			xmlEle.appendChild(m_childNode.toXML());
		}
                return(xmlEle);
        }
        function fromXML(inXML){
		m_PKey=inXML.getAttribute("pkey");
		m_relationType=inXML.getAttribute("relationtype");
		if (m_relationType == "") { m_relationType="main"; }
		m_displayDom.setAttribute("id","mmNodeRel_" + m_PKey);

		var parentNodePKey=inXML.getAttribute("parentnodepkey");
		var childNodePKey=inXML.getAttribute("childnodepkey");
		m_parentNode=document.getElementById("mmNode_" + parentNodePKey);

		if (inXML.childNodes.length > 0){
			// Main-Relation
			m_childNode=new node().fromXML(inXML.firstChild);
		} else {
			// free links don't create nodes
			m_childNode=document.getElementById("mmNode_" + childNodePKey);
			if (m_childNode==null) { alert("Error: Assertion failed,\ncan't backlink NodePKey _ " + childNodePKey + "_"); }
		}
		m_childNode.addNodeRelation(m_displayDom);
		m_parentNode.addNodeRelation(m_displayDom);

		return(construct());
        }
}