			a rectangle, by multiplying width and height.
				</p>
				<pre class="example-js">
var NS = "http://datashapes.org/js/tests/rules/rectangle.test#";

function computeArea($this) {
	var width = getProperty($this, "width");
	var height = getProperty($this, "height");
	var area = TermFactory.literal(width.lex * height.lex, width.datatype);
	var areaProperty = TermFactory.namedNode(NS + "area");
	return [ [$this, areaProperty, area] ]; 
}

function getProperty($this, name) {
	var it = $data.find($this, TermF