public function isMultiple()
    {
        $returnValue = (bool) false;

        if(is_null($this->multiple )){
        	$multipleProperty = $this->getProperty(GenerisRdf::PROPERTY_MULTIPLE);
			$multiple = $this->getOnePropertyValue($multipleProperty);
			 
			if(is_null($multiple)){
				$returnValue = false;
			}
			else{
				$returnValue = ($multiple->getUri() == GenerisRdf::GENERIS_TRUE);
			}
        	$this->multiple = $returnValue;
        }
 
        $returnValue = $this->multiple;
        return (bool) $returnValue;
    }